CVE-2026-66035
CVE-2026-66035
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.
Fixes and workarounds
Fix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: [email protected]Fix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: [email protected]Fix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: [email protected]Affected products and versions
| Product | Versions | Authority |
|---|---|---|
| libssh2 libssh2 |
≤ 1.11.1 (affected, custom) | NVD |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
NVD applicability configurations (1)
These expressions retain AND/OR operators, negation, and required environmental products. A listed product is not sufficient to establish exposure when additional conditions apply.
[
{
"negate": false,
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:a:libssh2:libssh2:*:*:*:*:*:*:*:*",
"versionEndIncluding": "1.11.1",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
],
"operator": "OR"
}
]CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 4.0 / 7.7 high |
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 | NVD: [email protected] |
| 3.1 / 7.5 high |
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H | NVD: [email protected] |
Exploit evidence
No exploit evidence in collected sources. This is not proof of no exploitation.
References
- https://github.com/libssh2/libssh2/commit/42e33d81577ed4b95d4b4f6f845e5ee8efe5eeb4[email protected] · Patch
- https://github.com/libssh2/libssh2/pull/2198[email protected] · Issue Tracking, Patch
- https://www.vulncheck.com/advisories/libssh2-heap-buffer-overflow-via-etm-cipher-negotiation[email protected] · Patch, Third Party Advisory
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