CVE-2026-66034
libssh2 Heap Out-of-Bounds Read via publickey subsystem
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.
Fixes and workarounds
Fix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: CNA: VulnCheckFix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: CNA: VulnCheckFix
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 libssh2/libssh2
github |
≥ 0; ≤ 1.11.1 (affected, semver) a13bb6c773f0d55ad1628cede57e99803cd898d9 (unaffected, git) Other versions: affected |
CNA: VulnCheck |
| SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) Siemens |
≥ V3.1.7; < * (affected, custom)
Other versions: unknown |
ADP: siemens-SADP |
| SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) Siemens |
≥ V3.1.7; < * (affected, custom)
Other versions: unknown |
ADP: siemens-SADP |
| SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) Siemens |
≥ V3.1.7; < * (affected, custom)
Other versions: unknown |
ADP: siemens-SADP |
| SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) Siemens |
≥ V3.1.7; < * (affected, custom)
Other versions: unknown |
ADP: siemens-SADP |
| SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) Siemens |
≥ V3.1.7; < * (affected, custom)
Other versions: unknown |
ADP: siemens-SADP |
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 | CNA: VulnCheck |
| 3.1 / 7.5 high |
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H | CNA: VulnCheck |
| 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/pull/2202CNA: VulnCheck · issue-tracking, patch
- https://github.com/libssh2/libssh2/commit/a13bb6c773f0d55ad1628cede57e99803cd898d9CNA: VulnCheck · patch
- https://www.vulncheck.com/advisories/libssh2-heap-out-of-bounds-read-via-publickey-subsystemCNA: VulnCheck · third-party-advisory
- https://cert-portal.siemens.com/productcert/html/ssa-457936.htmlADP: siemens-SADP
- https://github.com/libssh2/libssh2/commit/a13bb6c773f0d55ad1628cede57e99803cd898d9[email protected] · Patch
- https://github.com/libssh2/libssh2/pull/2202[email protected] · Issue Tracking, Patch
- https://www.vulncheck.com/advisories/libssh2-heap-out-of-bounds-read-via-publickey-subsystem[email protected] · Patch, Third Party Advisory
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