Buffer overflow in Vanhauser-Thc Thc-Hydra

CVE-2026-56766

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.

Vulnerability class: Buffer Overflow

Published · last modified .

CVSS v3 metric

CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.024 (83.6th percentile), scored .

Low probability of exploitation in the next 30 days, but still tracked. 84th percentile — 83.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-56766: held from 0.024 to 0.024.

EPSS over last 30 days · oldest: 0.024 · newest: 0.024 · change: 0.000

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-56766?
CVE-2026-56766 is a high-severity vulnerability in Vanhauser-Thc Thc-Hydra, classified under Stack-based Buffer Overflow. CVSS score: 8.8/10. Published 2026-06-25.
How severe is CVE-2026-56766?
High severity. CVSS v3 base score is 8.8 out of 10.