CVE-2026-4873

Published May 13, 2026

Last updated 24 days ago

CVSS medium 5.9
Libcurl

Overview

Description
A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.
Source
2499f714-1537-4658-8207-48ae4bb9eae9
NVD status
Analyzed
Products
curl

Risk scores

CVSS 3.1

Type
Secondary
Base score
5.9
Impact score
3.6
Exploitability score
2.2
Vector string
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Severity
MEDIUM

Weaknesses

nvd@nist.gov
CWE-295
134c704f-9b21-4f2e-91b3-4a467353bcc0
CWE-319

Social media

Hype score
Not currently trending

Configurations

Related CVEs

  1. Successfully using libcurl to do a transfer over a specific HTTP proxy (`proxyA`) with **Digest** authentication and then changing the proxy host to a second one (`proxyB`) for a second transfer, reusing the same handle, makes libcurl wrongly pass on the `Proxy-Authorization:` header field meant for `proxyA`, to `proxyB`.•CVE-2026-7168
  2. 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 fails to detect OCSP problems and instead wrongly consider the response as fine.•CVE-2026-7009
  3. libcurl might in some circumstances reuse the wrong connection for SMB(S) transfers. libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead. When reusing a connection a range of criteria must be met. Due to a logical error in the code, a network transfer operation that was requested by an application could wrongfully reuse an existing SMB connection to the same server that was using a different 'share' than the new subsequent transfer should. This could in unlucky situations lead to the download of the wrong file or the upload of a file to the wrong place. When this happens, the same credentials are used and the server name is the same.•CVE-2026-5773
  4. curl might erroneously pass on credentials for a first proxy to a second proxy. This can happen when the following conditions are true: 1. curl is setup to use specific different proxies for different URL schemes 2. the first proxy needs credentials 3. the second proxy uses no credentials 4. while using the first proxy (using say `http://`), curl is asked to follow a redirect to a URL using another scheme (say `https://`), accessed using a second, different, proxy•CVE-2026-6253
  5. When asked to both use a `.netrc` file for credentials and to follow HTTP redirects, libcurl could leak the password used for the first host to the followed-to host under certain circumstances.•CVE-2026-6429

References

Sources include official advisories and independent security research.