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Vulnerability record · CVE-2026-56766 · published 25 June 2026

CVE-2026-56766: Stack-based buffer overflow vulnerability

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.

8.6 CVSS 4.0 High EPSS 2.4% · top 16.4% CWE-121 · Stack-based buffer overflow Deferred
8.6CVSS 4.0 base score
2.4%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
2References
14 Jul 2026Last modified by NVD

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.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

LinkTags
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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Source: NIST National Vulnerability Database (record CVE-2026-56766), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.