vanhauser-thc thc-hydra up to 9.7 Urlenum stack-based overflow

Summaryinfo

A vulnerability identified as critical has been detected in vanhauser-thc thc-hydra up to 9.7. Impacted is an unknown function of the component Urlenum Module. This manipulation causes stack-based overflow. This vulnerability is registered as CVE-2026-56766. Remote exploitation of the attack is possible. No exploit is available. Applying a patch is the recommended action to fix this issue.

Detailsinfo

A vulnerability classified as critical was found in vanhauser-thc thc-hydra up to 9.7. Affected by this vulnerability is some unknown functionality of the component Urlenum Module. The manipulation with an unknown input leads to a stack-based overflow vulnerability. The CWE definition for the vulnerability is CWE-121. A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function). As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

The weakness was published by Tristan Madani as 9cc84c20e75f5fef6bb1790bb9ada2afad2204e2. The advisory is shared at github.com. This vulnerability is known as CVE-2026-56766 since 06/22/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Neither technical details nor an exploit are publicly available.

Applying the patch 9cc84c20e75f5fef6bb1790bb9ada2afad2204e2 is able to eliminate this problem. The bugfix is ready for download at github.com.

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Productinfo

Vendor

• vanhauser-thc

Name

• thc-hydra

Version

• 9.0
• 9.1
• 9.2
• 9.3
• 9.4
• 9.5
• 9.6
• 9.7

License

• open-source

Website

• Product: https://github.com/vanhauser-thc/thc-hydra/

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