CVE-2026-66034

Published Jul 24, 2026

Last updated 8 days ago

CVSS high 7.7
SSH

Overview

Description
libssh2 through 1.11.1, fixed in commit a13bb6c, contains a missing bounds check vulnerability that allows a malicious SSH server to trigger an arbitrary-length heap out-of-bounds read and a free of an uninitialized pointer via the publickey subsystem. In libssh2_publickey_list_fetch(), the version 1 response parser reads a server-controlled comment_len value and advances the parse pointer without verifying sufficient bytes remain in the buffer, causing the out-of-bounds read to leak heap pointers from adjacent allocations defeating ASLR, followed by heap allocator state corruption when the error cleanup path frees an uninitialized pointer from a non-zeroed realloc() region.
Source
disclosure@vulncheck.com
NVD status
Analyzed
Products
libssh2

Risk scores

CVSS 4.0

Type
Secondary
Base score
7.7
Impact score
-
Exploitability score
-
Vector string
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Severity
HIGH

CVSS 3.1

Type
Secondary
Base score
7.5
Impact score
5.9
Exploitability score
1.6
Vector string
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
Severity
HIGH

Weaknesses

disclosure@vulncheck.com
CWE-125

Social media

Hype score
Not currently trending

  1. libssh2 の脆弱性 CVE-2026-66032／66033／66034／66035 が FIX：悪意の SSH サーバによるクライアント破壊 https://t.co/dNUXjLPR9L libssh2 の脆弱性 CVE-2026-66032／CVE-2026-66033／CVE-2026-66034／CVE-2026-66035

    @iototsecnews

    5 Aug 2026

    86 Impressions

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  2. 🔴 libssh2'de keşfedilen dört kritik güvenlik açığı (CVE-2026-66032, CVE-2026-66033, CVE-2026-66034 ve CVE-2026-66035), kötü niyetli bir SSH/SFTP sunucusunun istemci uygulamalarında bellek bozulmasına, uygulamanın çökmesine ve bazı senaryolarda potansiyel uzaktan

    @ridvanyagli

    28 Jul 2026

    68 Impressions

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    0 Quotes

Configurations

Related CVEs

  1. libssh2 through 1.11.1, fixed in commit 5e47761, contains a double-free vulnerability in the sftp_open() function in src/sftp.c that allows a malicious SSH server to corrupt the heap of any authenticated client opening an SFTP session. When a server responds to SSH_FXP_OPEN with SSH_FXP_STATUS containing FX_OK, the response data buffer is freed, and if a subsequent sftp_packet_require() call returns a specific error such as LIBSSH2_ERROR_CHANNEL_PACKET_EXCEEDED, the same pointer is freed a second time, enabling tcache dup conditions on glibc systems that allow overlapping allocations and function pointer overwrites.•CVE-2026-66032
  2. libssh2 through 1.11.1, fixed in commit 42e33d8, contains a pre-authentication heap buffer overflow vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by sending a packet with a packet_length smaller than the cipher's block size during Encrypt-then-MAC cipher negotiation. In the fullpacket() function in src/transport.c, the ETM path allocates a buffer of packet_length bytes but copies blocksize minus one bytes via memcpy, causing an overflow that on 32-bit glibc writes attacker-controlled bytes into an adjacent chunk's SIZE field, enabling tcache bin confusion, overlapping live objects, and function pointer overwrite during the session handshake before authentication.•CVE-2026-66035
  3. libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server to crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an out-of-bounds read and a memcpy call with a near-SIZE_MAX length argument, causing immediate process crash before any authentication occurs.•CVE-2026-66033
  4. A Missing Authentication vulnerability was discovered in the SSH keys synchronization endpoint. An unauthenticated attacker can send a request to the SSH keys synchronization endpoint and obtain the list of users that have uploaded their public SSH keys, their groups, and the uploaded public SSH keys.•CVE-2026-31983
  5. libssh2 through 1.11.1 reads an attacker-controlled 32-bit attribute count from a publickey-subsystem response and uses it in the allocation num_attrs * sizeof(libssh2_publickey_attribute) without bounds checking, so on 32-bit platforms the multiplication overflows to an undersized buffer. A malicious SSH server can then drive the attribute-parsing loop to write past the allocation, causing a heap buffer overflow in a connecting libssh2 client.•CVE-2026-58050

References

Sources include official advisories and independent security research.