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CVE-2026-66033

7.5 · HIGH

libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH serve…

Published Jul 24, 2026CWE-125EPSS 0.58%

Overview

CVE-2026-66033 is a high-severity vulnerability. It was published on July 24, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server to crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an out-of-bounds read and a memcpy call with a near-SIZE_MAX length argument, causing immediate process crash before any authentication occurs.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2e6GitHubgithub.com/libssh2/libssh2/pull/2401Refwww.vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cipher-negotiation

How CyberStrike helps

Frequently asked questions

What is CVE-2026-66033?

CVE-2026-66033 is a high-severity vulnerability. It was published on July 24, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-66033?

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-66033?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-66033?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-66033 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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