How severe is CVE-2026-56766?

CVE-2026-56766 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-56766 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (68th percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2026-56766?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-56766 have an EU (EUVD) identifier?

Yes. CVE-2026-56766 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-39515.

When was CVE-2026-56766 published?

CVE-2026-56766 was published on 2026-06-25.

CVE-2026-56766

CVE-2026-56766 is a high-severity vulnerability with a CVSS 3.x base score of 8.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-121.

Key facts

Severity: High (CVSS 3.x base score 8.8)
CVSS v4: 8.6
EPSS exploit prediction: 1% (68th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-39515
Weakness: CWE-121
Published: 2026-06-25
Last modified: 2026-06-25

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-56766?: CVE-2026-56766 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-56766 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (68th percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-56766?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-56766 have an EU (EUVD) identifier?: Yes. CVE-2026-56766 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-39515.
When was CVE-2026-56766 published?: CVE-2026-56766 was published on 2026-06-25.

References

Other CWE-121 (Stack-based Buffer Overflow) vulnerabilities

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CVE-2026-12846 — Critical (CVSS 10.0): GV-I/O Box 4E is a smart embedded device with 4 input and 4 relays output that can be controlled over Ethernet and…
CVE-2026-12485 — Critical (CVSS 10.0): GV-I/O Box 4E is a smart embedded device with 4 input and 4 relays output that can be controlled over Ethernet and…
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