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

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 2.4% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-06-25 · updated 2026-10-25
Weakness: CWE-121

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 products

vanhauser-thc thc-hydra: through 9.7

References

https://github.com/vanhauser-thc/thc-hydra/commit/9cc84c20e75f5fef6bb1790bb9ada2afad2204e2
https://www.vulncheck.com/advisories/hydra-stack-buffer-overflow-in-ntlm-authentication-handler

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