High [CVE-2026-56766] Remote Code Execution via NTLM Authentication Stack Buffer Overflow
This high-severity Red Hat Linux advisory covers CVE-2026-56766.
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Summary
Hydra through 9.7, fixed in commit 9cc84c2, contains a stack buffer overflow in NTLM authentication across SMTP, POP3, IMAP, NNTP, HTTP, HTTP-Proxy, and HTTP-Proxy-Urlenum modules when processing malicious NTLM Type-2 challenges.
A malicious server can send a crafted NTLM Type-2 challenge with an excessively long domain string, causing base64-encoded response data to overflow a 500-byte stack buffer by 18 to 330 bytes, enabling remote code execution on systems without stack protection. A flaw was found in Hydra.
An important security flaw in the Hydra tool lets a malicious server take control of your computer. For an attack to work, you must be tricked into actively connecting Hydra to the attacker's rigged server.
The standard security features built into Red Hat systems act as a safety net, making it very difficult for attackers to actually exploit this issue. Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H).
Weakness: CWE-120.
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 21 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 21 days ago·verify at source
Mitigation checklist
- Ensure your system's built-in security features are active and up to date. These standard protections automatically look for memory errors, causing the application to safely shut down the moment it receives too much data, completely blocking any harmful commands from running.
Official advisory · high-confidence parse· fetched 21 days ago·verify at source
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