CVE-2026-66034
libssh2 Heap Out-of-Bounds Read via publickey subsystem
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.
INFO
Published Date :
July 24, 2026, 5:17 p.m.
Last Modified :
July 30, 2026, 3:44 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | 83251b91-4cc7-4094-a5c7-464a1b83ea10 | ||||
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 4.0 | HIGH | 83251b91-4cc7-4094-a5c7-464a1b83ea10 | ||||
| CVSS 4.0 | HIGH | [email protected] |
Solution
- Update libssh2 library to patched version.
- Apply commit a13bb6c to libssh2.
- Validate buffer bounds checks.
- Ensure proper memory initialization.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-66034.
| URL | Resource |
|---|---|
| https://github.com/libssh2/libssh2/commit/a13bb6c773f0d55ad1628cede57e99803cd898d9 | Patch |
| https://github.com/libssh2/libssh2/pull/2202 | Issue Tracking Patch |
| https://www.vulncheck.com/advisories/libssh2-heap-out-of-bounds-read-via-publickey-subsystem | Patch Third Party Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-66034 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-66034
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-66034 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-66034 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Jul. 30, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:libssh2:libssh2:*:*:*:*:*:*:*:* versions up to (including) 1.11.1 Added Reference Type VulnCheck: https://github.com/libssh2/libssh2/commit/a13bb6c773f0d55ad1628cede57e99803cd898d9 Types: Patch Added Reference Type VulnCheck: https://github.com/libssh2/libssh2/pull/2202 Types: Issue Tracking, Patch Added Reference Type VulnCheck: https://www.vulncheck.com/advisories/libssh2-heap-out-of-bounds-read-via-publickey-subsystem Types: Patch, Third Party Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 25, 2026
Action Type Old Value New Value Changed SSVC {'id': 'CVE-2026-66034', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-24T17:31:09.552541Z'} {'id': 'CVE-2026-66034', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-24T00:00:00+00:00'} -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 24, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-66034', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-24T17:31:09.552541Z'} -
New CVE Received by [email protected]
Jul. 24, 2026
Action Type Old Value New Value Added Affected [{'repo': 'https://github.com/libssh2/libssh2', 'vendor': 'libssh2', 'product': 'libssh2', 'versions': [{'status': 'affected', 'version': '0', 'versionType': 'semver', 'lessThanOrEqual': '1.11.1'}, {'status': 'unaffected', 'version': 'a13bb6c773f0d55ad1628cede57e99803cd898d9', 'versionType': 'git'}], 'packageURL': 'pkg:github/libssh2/libssh2', 'defaultStatus': 'affected'}] Added 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. Added CVSS V4.0 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 Added CVSS V3.1 AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H Added CWE CWE-125 Added CWE CWE-908 Added Reference https://github.com/libssh2/libssh2/commit/a13bb6c773f0d55ad1628cede57e99803cd898d9 Added Reference https://github.com/libssh2/libssh2/pull/2202 Added Reference https://www.vulncheck.com/advisories/libssh2-heap-out-of-bounds-read-via-publickey-subsystem