Medium [CVE-2026-66034] Information disclosure and potential arbitrary code execution via heap out-of-bounds read
This medium-severity Red Hat Linux advisory covers CVE-2026-66034 affecting Red Hat Enterprise Linux 7 Extended Lifecycle Support, Red Hat Hardened Images, Red Hat Enterprise Linux 6.
Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.
VulniPulse record published Record updated
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Summary
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.
A missing bounds check in the libssh2 publickey subsystem allows malicious SSH servers to trigger a client-side out-of-bounds read, leaking heap pointers that could enable security bypasses, denial of service, or code execution.
While requiring user interaction to connect to a compromised server and having high attack complexity, successful exploitation could leak heap pointers, potentially aiding in ASLR bypass and leading to arbitrary code execution or denial of service on Red Hat Hardened Images.
Red Hat severity: Moderate — CVSS 5.9 (CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:H). Weakness: CWE-125.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.
Official advisory · high-confidence parse· fetched 2 days ago·verify at source
- 1.11.1
- libssh2-0:1.8.0-4.el7_9.2
- libssh2-main-1.11.1-10.2.hum1
- RHSA-2026:61752
- RHSA-2026:46927
Official advisory · high-confidence parse· fetched 2 days ago·verify at source
Mitigation checklist
- To mitigate this, strictly avoid connecting to untrusted SSH servers and enforce this policy using outbound network firewalls to block unknown IP addresses. For defense-in-depth, utilize OS-level memory protections and service sandboxing to contain any accidental exposure.
Official advisory · high-confidence parse· fetched 2 days ago·verify at source
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