Curl vulnerabilities

curl's WebSocket code did not update the 32-bit mask pattern for each new outgoing frame as the specification says. Instead it used a fixed mask that persisted and was used throughout the entire connection. A predictable mask pattern allows for a malicious server to induce traffic between the two communicating parties that could be interpreted by an involved proxy (configured or transparent) as genuine, real, HTTP traffic with content and thereby poison its cache. That cached poisoned content could then be served to all users of that proxy.

Due to a mistake in libcurl's WebSocket code, a malicious server can send a particularly crafted packet which makes libcurl get trapped in an endless busy-loop. There is no other way for the application to escape or exit this loop other than killing the thread/process. This might be used to DoS libcurl-using application.

libcurl supports *pinning* of the server certificate public key for HTTPS transfers. Due to an omission, this check is not performed when connecting with QUIC for HTTP/3, when the TLS backend is wolfSSL. Documentation says the option works with wolfSSL, failing to specify that it does not for QUIC and HTTP/3. Since pinning makes the transfer succeed if the pin is fine, users could unwittingly connect to an impostor server without noticing.

libcurl accidentally skips the certificate verification for QUIC connections when connecting to a host specified as an IP address in the URL. Therefore, it does not detect impostors or man-in-the-middle attacks.

When libcurl is asked to perform automatic gzip decompression of content-encoded HTTP responses with the `CURLOPT_ACCEPT_ENCODING` option, **using zlib 1.2.0.3 or older**, an attacker-controlled integer overflow would make libcurl perform a buffer overflow.

libcurl would wrongly close the same eventfd file descriptor twice when taking down a connection channel after having completed a threaded name resolve.

When asked to use a `.netrc` file for credentials **and** to follow HTTP redirects, curl could leak the password used for the first host to the followed-to host under certain circumstances. This flaw only manifests itself if the netrc file has a `default` entry that omits both login and password. A rare circumstance.

When asked to both use a `.netrc` file for credentials and to follow HTTP redirects, curl could leak the password used for the first host to the followed-to host under certain circumstances. This flaw only manifests itself if the netrc file has an entry that matches the redirect target hostname but the entry either omits just the password or omits both login and password.

When curl is asked to use HSTS, the expiry time for a subdomain might overwrite a parent domain's cache entry, making it end sooner or later than otherwise intended. This affects curl using applications that enable HSTS and use URLs with the insecure `HTTP://` scheme and perform transfers with hosts like `x.example.com` as well as `example.com` where the first host is a subdomain of the second host. (The HSTS cache either needs to have been populated manually or there needs to have been previous HTTPS accesses done as the cache needs to have entries for the domains involved to trigger this problem.) When `x.example.com` responds with `Strict-Transport-Security:` headers, this bug can make the subdomain's expiry timeout *bleed over* and get set for the parent domain `example.com` in curl's HSTS cache. The result of a triggered bug is that HTTP accesses to `example.com` get converted to HTTPS for a different period of time than what was asked for by the origin server. If `example.com` for example stops supporting HTTPS at its expiry time, curl might then fail to access `http://example.com` until the (wrongly set) timeout expires. This bug can also expire the parent's entry *earlier*, thus making curl inadvertently switch back to insecure HTTP earlier than otherwise intended.

When curl is told to use the Certificate Status Request TLS extension, often referred to as OCSP stapling, to verify that the server certificate is valid, it might fail to detect some OCSP problems and instead wrongly consider the response as fine. If the returned status reports another error than 'revoked' (like for example 'unauthorized') it is not treated as a bad certficate.

libcurl's ASN1 parser code has the `GTime2str()` function, used for parsing an ASN.1 Generalized Time field. If given an syntactically incorrect field, the parser might end up using -1 for the length of the *time fraction*, leading to a `strlen()` getting performed on a pointer to a heap buffer area that is not (purposely) null terminated. This flaw most likely leads to a crash, but can also lead to heap contents getting returned to the application when [CURLINFO_CERTINFO](https://curl.se/libcurl/c/CURLINFO_CERTINFO.html) is used.

libcurl's ASN1 parser has this utf8asn1str() function used for parsing an ASN.1 UTF-8 string. Itcan detect an invalid field and return error. Unfortunately, when doing so it also invokes `free()` on a 4 byte localstack buffer. Most modern malloc implementations detect this error and immediately abort. Some however accept the input pointer and add that memory to its list of available chunks. This leads to the overwriting of nearby stack memory. The content of the overwrite is decided by the `free()` implementation; likely to be memory pointers and a set of flags. The most likely outcome of exploting this flaw is a crash, although it cannot be ruled out that more serious results can be had in special circumstances.

libcurl did not check the server certificate of TLS connections done to a host specified as an IP address, when built to use mbedTLS. libcurl would wrongly avoid using the set hostname function when the specified hostname was given as an IP address, therefore completely skipping the certificate check. This affects all uses of TLS protocols (HTTPS, FTPS, IMAPS, POPS3, SMTPS, etc).

When an application tells libcurl it wants to allow HTTP/2 server push, and the amount of received headers for the push surpasses the maximum allowed limit (1000), libcurl aborts the server push. When aborting, libcurl inadvertently does not free all the previously allocated headers and instead leaks the memory. Further, this error condition fails silently and is therefore not easily detected by an application.

libcurl skips the certificate verification for a QUIC connection under certain conditions, when built to use wolfSSL. If told to use an unknown/bad cipher or curve, the error path accidentally skips the verification and returns OK, thus ignoring any certificate problems.

When a protocol selection parameter option disables all protocols without adding any then the default set of protocols would remain in the allowed set due to an error in the logic for removing protocols. The below command would perform a request to curl.se with a plaintext protocol which has been explicitly disabled. curl --proto -all,-http http://curl.se The flaw is only present if the set of selected protocols disables the entire set of available protocols, in itself a command with no practical use and therefore unlikely to be encountered in real situations. The curl security team has thus assessed this to be low severity bug.

curl inadvertently kept the SSL session ID for connections in its cache even when the verify status (*OCSP stapling*) test failed. A subsequent transfer to the same hostname could then succeed if the session ID cache was still fresh, which then skipped the verify status check.

When saving HSTS data to an excessively long file name, curl could end up removing all contents, making subsequent requests using that file unaware of the HSTS status they should otherwise use.

This flaw allows a malicious HTTP server to set "super cookies" in curl that are then passed back to more origins than what is otherwise allowed or possible. This allows a site to set cookies that then would get sent to different and unrelated sites and domains. It could do this by exploiting a mixed case flaw in curl's function that verifies a given cookie domain against the Public Suffix List (PSL). For example a cookie could be set with `domain=co.UK` when the URL used a lower case hostname `curl.co.uk`, even though `co.uk` is listed as a PSL domain.

This flaw allows an attacker to insert cookies at will into a running program using libcurl, if the specific series of conditions are met. libcurl performs transfers. In its API, an application creates "easy handles" that are the individual handles for single transfers. libcurl provides a function call that duplicates en easy handle called [curl_easy_duphandle](https://curl.se/libcurl/c/curl_easy_duphandle.html). If a transfer has cookies enabled when the handle is duplicated, the cookie-enable state is also cloned - but without cloning the actual cookies. If the source handle did not read any cookies from a specific file on disk, the cloned version of the handle would instead store the file name as `none` (using the four ASCII letters, no quotes). Subsequent use of the cloned handle that does not explicitly set a source to load cookies from would then inadvertently load cookies from a file named `none` - if such a file exists and is readable in the current directory of the program using libcurl. And if using the correct file format of course.

This flaw makes curl overflow a heap based buffer in the SOCKS5 proxy handshake. When curl is asked to pass along the host name to the SOCKS5 proxy to allow that to resolve the address instead of it getting done by curl itself, the maximum length that host name can be is 255 bytes. If the host name is detected to be longer, curl switches to local name resolving and instead passes on the resolved address only. Due to this bug, the local variable that means "let the host resolve the name" could get the wrong value during a slow SOCKS5 handshake, and contrary to the intention, copy the too long host name to the target buffer instead of copying just the resolved address there. The target buffer being a heap based buffer, and the host name coming from the URL that curl has been told to operate with.

When curl retrieves an HTTP response, it stores the incoming headers so that they can be accessed later via the libcurl headers API. However, curl did not have a limit in how many or how large headers it would accept in a response, allowing a malicious server to stream an endless series of headers and eventually cause curl to run out of heap memory.

Integer overflow vulnerability in tool_operate.c in curl 7.65.2 via a large value as the retry delay. NOTE: many parties report that this has no direct security impact on the curl user; however, it may (in theory) cause a denial of service to associated systems or networks if, for example, --retry-delay is misinterpreted as a value much smaller than what was intended. This is not especially plausible because the overflow only happens if the user was trying to specify that curl should wait weeks (or longer) before trying to recover from a transient error.

An information disclosure vulnerability exists in curl <v8.1.0 when doing HTTP(S) transfers, libcurl might erroneously use the read callback (`CURLOPT_READFUNCTION`) to ask for data to send, even when the `CURLOPT_POSTFIELDS` option has been set, if the same handle previously wasused to issue a `PUT` request which used that callback. This flaw may surprise the application and cause it to misbehave and either send off the wrong data or use memory after free or similar in the second transfer. The problem exists in the logic for a reused handle when it is (expected to be) changed from a PUT to a POST.

A use after free vulnerability exists in curl <v8.1.0 in the way libcurl offers a feature to verify an SSH server's public key using a SHA 256 hash. When this check fails, libcurl would free the memory for the fingerprint before it returns an error message containing the (now freed) hash. This flaw risks inserting sensitive heap-based data into the error message that might be shown to users or otherwise get leaked and revealed.

An authentication bypass vulnerability exists in libcurl <8.0.0 in the FTP connection reuse feature that can result in wrong credentials being used during subsequent transfers. Previously created connections are kept in a connection pool for reuse if they match the current setup. However, certain FTP settings such as CURLOPT_FTP_ACCOUNT, CURLOPT_FTP_ALTERNATIVE_TO_USER, CURLOPT_FTP_SSL_CCC, and CURLOPT_USE_SSL were not included in the configuration match checks, causing them to match too easily. This could lead to libcurl using the wrong credentials when performing a transfer, potentially allowing unauthorized access to sensitive information.

A path traversal vulnerability exists in curl <8.0.0 SFTP implementation causes the tilde (~) character to be wrongly replaced when used as a prefix in the first path element, in addition to its intended use as the first element to indicate a path relative to the user's home directory. Attackers can exploit this flaw to bypass filtering or execute arbitrary code by crafting a path like /~2/foo while accessing a server with a specific user.

A vulnerability in input validation exists in curl <8.0 during communication using the TELNET protocol may allow an attacker to pass on maliciously crafted user name and "telnet options" during server negotiation. The lack of proper input scrubbing allows an attacker to send content or perform option negotiation without the application's intent. This vulnerability could be exploited if an application allows user input, thereby enabling attackers to execute arbitrary code on the system.

An allocation of resources without limits or throttling vulnerability exists in curl <v7.88.0 based on the "chained" HTTP compression algorithms, meaning that a server response can be compressed multiple times and potentially with differentalgorithms. The number of acceptable "links" in this "decompression chain" wascapped, but the cap was implemented on a per-header basis allowing a maliciousserver to insert a virtually unlimited number of compression steps simply byusing many headers. The use of such a decompression chain could result in a "malloc bomb", making curl end up spending enormous amounts of allocated heap memory, or trying to and returning out of memory errors.

A cleartext transmission of sensitive information vulnerability exists in curl <v7.88.0 that could cause HSTS functionality to behave incorrectly when multiple URLs are requested in parallel. Using its HSTS support, curl can be instructed to use HTTPS instead of using an insecure clear-text HTTP step even when HTTP is provided in the URL. This HSTS mechanism would however surprisingly fail when multiple transfers are done in parallel as the HSTS cache file gets overwritten by the most recentlycompleted transfer. A later HTTP-only transfer to the earlier host name would then *not* get upgraded properly to HSTS.

A cleartext transmission of sensitive information vulnerability exists in curl <v7.88.0 that could cause HSTS functionality fail when multiple URLs are requested serially. Using its HSTS support, curl can be instructed to use HTTPS instead of usingan insecure clear-text HTTP step even when HTTP is provided in the URL. ThisHSTS mechanism would however surprisingly be ignored by subsequent transferswhen done on the same command line because the state would not be properlycarried on.

A use after free vulnerability exists in curl <7.87.0. Curl can be asked to *tunnel* virtually all protocols it supports through an HTTP proxy. HTTP proxies can (and often do) deny such tunnel operations. When getting denied to tunnel the specific protocols SMB or TELNET, curl would use a heap-allocated struct after it had been freed, in its transfer shutdown code path.

A vulnerability exists in curl <7.87.0 HSTS check that could be bypassed to trick it to keep using HTTP. Using its HSTS support, curl can be instructed to use HTTPS instead of using an insecure clear-text HTTP step even when HTTP is provided in the URL. However, the HSTS mechanism could be bypassed if the host name in the given URL first uses IDN characters that get replaced to ASCII counterparts as part of the IDN conversion. Like using the character UTF-8 U+3002 (IDEOGRAPHIC FULL STOP) instead of the common ASCII full stop (U+002E) `.`. Then in a subsequent request, it does not detect the HSTS state and makes a clear text transfer. Because it would store the info IDN encoded but look for it IDN decoded.

curl can be told to parse a `.netrc` file for credentials. If that file endsin a line with 4095 consecutive non-white space letters and no newline, curlwould first read past the end of the stack-based buffer, and if the readworks, write a zero byte beyond its boundary.This will in most cases cause a segfault or similar, but circumstances might also cause different outcomes.If a malicious user can provide a custom netrc file to an application or otherwise affect its contents, this flaw could be used as denial-of-service.

When doing HTTP(S) transfers, libcurl might erroneously use the read callback (`CURLOPT_READFUNCTION`) to ask for data to send, even when the `CURLOPT_POSTFIELDS` option has been set, if the same handle previously was used to issue a `PUT` request which used that callback. This flaw may surprise the application and cause it to misbehave and either send off the wrong data or use memory after free or similar in the subsequent `POST` request. The problem exists in the logic for a reused handle when it is changed from a PUT to a POST.

curl before 7.86.0 has a double free. If curl is told to use an HTTP proxy for a transfer with a non-HTTP(S) URL, it sets up the connection to the remote server by issuing a CONNECT request to the proxy, and then tunnels the rest of the protocol through. An HTTP proxy might refuse this request (HTTP proxies often only allow outgoing connections to specific port numbers, like 443 for HTTPS) and instead return a non-200 status code to the client. Due to flaws in the error/cleanup handling, this could trigger a double free in curl if one of the following schemes were used in the URL for the transfer: dict, gopher, gophers, ldap, ldaps, rtmp, rtmps, or telnet. The earliest affected version is 7.77.0.

In curl before 7.86.0, the HSTS check could be bypassed to trick it into staying with HTTP. Using its HSTS support, curl can be instructed to use HTTPS directly (instead of using an insecure cleartext HTTP step) even when HTTP is provided in the URL. This mechanism could be bypassed if the host name in the given URL uses IDN characters that get replaced with ASCII counterparts as part of the IDN conversion, e.g., using the character UTF-8 U+3002 (IDEOGRAPHIC FULL STOP) instead of the common ASCII full stop of U+002E (.). The earliest affected version is 7.77.0 2021-05-26.

When curl is used to retrieve and parse cookies from a HTTP(S) server, itaccepts cookies using control codes that when later are sent back to a HTTPserver might make the server return 400 responses. Effectively allowing a"sister site" to deny service to all siblings.

When curl < 7.84.0 does FTP transfers secured by krb5, it handles message verification failures wrongly. This flaw makes it possible for a Man-In-The-Middle attack to go unnoticed and even allows it to inject data to the client.

When curl < 7.84.0 saves cookies, alt-svc and hsts data to local files, it makes the operation atomic by finalizing the operation with a rename from a temporary name to the final target file name.In that rename operation, it might accidentally *widen* the permissions for the target file, leaving the updated file accessible to more users than intended.

curl < 7.84.0 supports "chained" HTTP compression algorithms, meaning that a serverresponse can be compressed multiple times and potentially with different algorithms. The number of acceptable "links" in this "decompression chain" was unbounded, allowing a malicious server to insert a virtually unlimited number of compression steps.The use of such a decompression chain could result in a "malloc bomb", makingcurl end up spending enormous amounts of allocated heap memory, or trying toand returning out of memory errors.

A malicious server can serve excessive amounts of `Set-Cookie:` headers in a HTTP response to curl and curl < 7.84.0 stores all of them. A sufficiently large amount of (big) cookies make subsequent HTTP requests to this, or other servers to which the cookies match, create requests that become larger than the threshold that curl uses internally to avoid sending crazy large requests (1048576 bytes) and instead returns an error.This denial state might remain for as long as the same cookies are kept, match and haven't expired. Due to cookie matching rules, a server on `foo.example.com` can set cookies that also would match for `bar.example.com`, making it it possible for a "sister server" to effectively cause a denial of service for a sibling site on the same second level domain using this method.

Using its HSTS support, curl can be instructed to use HTTPS directly insteadof using an insecure clear-text HTTP step even when HTTP is provided in theURL. This mechanism could be bypassed if the host name in the given URL used atrailing dot while not using one when it built the HSTS cache. Or the otherway around - by having the trailing dot in the HSTS cache and *not* using thetrailing dot in the URL.

libcurl would reuse a previously created connection even when a TLS or SSHrelated option had been changed that should have prohibited reuse.libcurl keeps previously used connections in a connection pool for subsequenttransfers to reuse if one of them matches the setup. However, several TLS andSSH settings were left out from the configuration match checks, making themmatch too easily.

libcurl provides the `CURLOPT_CERTINFO` option to allow applications torequest details to be returned about a server's certificate chain.Due to an erroneous function, a malicious server could make libcurl built withNSS get stuck in a never-ending busy-loop when trying to retrieve thatinformation.

The curl URL parser wrongly accepts percent-encoded URL separators like '/'when decoding the host name part of a URL, making it a *different* URL usingthe wrong host name when it is later retrieved.For example, a URL like `http://example.com%2F127.0.0.1/`, would be allowed bythe parser and get transposed into `http://example.com/127.0.0.1/`. This flawcan be used to circumvent filters, checks and more.

libcurl wrongly allows cookies to be set for Top Level Domains (TLDs) if thehost name is provided with a trailing dot.curl can be told to receive and send cookies. curl's "cookie engine" can bebuilt with or without [Public Suffix List](https://publicsuffix.org/)awareness. If PSL support not provided, a more rudimentary check exists to atleast prevent cookies from being set on TLDs. This check was broken if thehost name in the URL uses a trailing dot.This can allow arbitrary sites to set cookies that then would get sent to adifferent and unrelated site or domain.

A use of incorrectly resolved name vulnerability fixed in 7.83.1 might remove the wrong file when `--no-clobber` is used together with `--remove-on-error`.

A insufficiently protected credentials vulnerability in fixed in curl 7.83.0 might leak authentication or cookie header data on HTTP redirects to the same host but another port number.

An information disclosure vulnerability exists in curl 7.65.0 to 7.82.0 are vulnerable that by using an IPv6 address that was in the connection pool but with a different zone id it could reuse a connection instead.