Vulnerability · Published Jun 25, 2026 · Assigned by VulnCheck

CVE-2026-56766Hydra - Stack Buffer Overflow in NTLM Authentication Handler

High 8.8

In plain English

A high-severity stack buffer overflow in thc-hydra from vanhauser-thc. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 2.4% (higher than 84% of all known vulnerabilities).

Severity (CVSS 3.1)8.8High

Exploit odds (30 days)2.4%top 15.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Ubuntu:22.04:LTS	hydra	no fix listed	UBUNTU-CVE-2026-56766
Ubuntu:24.04:LTS	hydra	no fix listed	UBUNTU-CVE-2026-56766
Ubuntu:25.10	hydra	no fix listed	UBUNTU-CVE-2026-56766
Ubuntu:26.04:LTS	hydra	no fix listed	UBUNTU-CVE-2026-56766
Ubuntu:26.10	hydra	no fix listed	UBUNTU-CVE-2026-56766

Affected products (as reported)

Vendor	Product	Versions
vanhauser-thc	thc-hydra	0 – through 9.7

Weakness: CWE-121 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

References

Patch Commit patch
https://www.vulncheck.com/advisories/hydra-stack-buffer-overflow-in-ntlm-authentication-handler third-party-advisory