Quick answers
- Is CVE-2026-66034 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-66034 being exploited in the wild.
- How severe is CVE-2026-66034?
- High severity, with a CVSS score of 7.5, published 24 July 2026.
- Which products and versions are affected?
- Libssh2 through 1.11.1.
- Is there a fix for CVE-2026-66034?
- A patch was published on 2026-07-04: Fix submitted via GitHub pull request 2202 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-66034 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-66034?
- Check whether you run Libssh2 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
A vulnerability exists in the libssh2_publickey_list_fetch() function within the publickey subsystem. The version 1 response parser fails to validate a server-controlled 'comment_len' value against the remaining buffer size before advancing the parse pointer. This leads to an arbitrary-length heap out-of-bounds read, which can be used to leak heap pointers and bypass ASLR. Additionally, the error cleanup path may attempt to free an uninitialized pointer from a non-zeroed realloc() region, resulting in heap corruption. Exploitation requires a user to connect to a malicious SSH server. The issue is fixed in commit a13bb6c.
Affected products
- libssh2 libssh2 through 1.11.1
Timeline
- 2026-07-04: patched: Fix submitted via GitHub pull request 2202
- 2026-07-24: disclosed: CVE-2026-66034 published