Cyber Resilience

CVE-2026-56766

HighPublic PoC

Published: 25 June 2026

Published
25 June 2026
Modified
25 June 2026
KEV Added
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Patch
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CVSS Score v4 8.6 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:X/V:X/RE:X/U:X
EPSS Score 0.0047 37.5th percentile
Risk Priority 55 floored blend · peak EPSS

Summary

CVE-2026-56766 is a high-severity Stack-based Buffer Overflow (CWE-121) vulnerability. Its CVSS base score is 8.6 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Client Execution (T1203); ranked at the 37.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

EU & UK References

Vulnerability details

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…

more

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.

CWE(s)
CWE-121

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
Why these techniques?

Stack buffer overflow in client-side NTLM handling allows RCE when connecting to a malicious server, directly matching client execution via crafted input.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

Affected Assets

Mitigating Controls

No mitigating controls mapped yet. The per-CVE control annotator has not reached this CVE.

References