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Vulnerabilities

Vulnerability · CVE-2026-66033

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 ma

Published Jul 24, 2026 · catalog updated Oct 21, 2026 · libssh2 through 1.11.1, fixed

Check if you run it

No confirmed exploitation is on record for CVE-2026-66033. EPSS is 0.58%. Act only if a listed version of libssh2 through 1.11.1, fixed is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (libssh2 through 1.11.1, fixed).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Unknown—
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.58%
Remediation
Advisory link
Affected products
Alpine:v3.21 libssh2 · Alpine:v3.22 libssh2 · Alpine:v3.23 libssh2 · Alpine:v3.24 libssh2

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • Alpine:v3.21 libssh20 → 1.11.1-r3
  • Alpine:v3.22 libssh20 → 1.11.1-r3
  • Alpine:v3.23 libssh20 → 1.11.1-r4
  • Alpine:v3.24 libssh20 → 1.11.1-r4

How to fix CVE-2026-66033

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-66033. EPSS is 0.58%. Act only if a listed version of libssh2 through 1.11.1, fixed is installed.

Which versions are affected?

Compare what you have installed with 0 → 1.11.1-r3, 0 → 1.11.1-r4. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.58%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Jul 24, 2026 · OpenSSF OSV / OSV Scanner

    Detected

    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

  2. Oct 20, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    libssh2 fixed in 1.11.1-r4

  3. Oct 20, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    libssh2 fixed in 1.11.1-r4

  4. Oct 20, 2026 · OpenSSF OSV / OSV Scanner

    Updated

    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

  5. Oct 21, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    libssh2 fixed in 1.11.1-r3; libssh2 fixed in 1.11.1-r3; libssh2 fixed in 1.11.1-r4; libssh2 fixed in 1.11.1-r4

  6. Oct 21, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    libssh2 fixed in 1.11.1-r3

  7. Oct 21, 2026 · OpenSSF OSV / OSV Scanner

    Updated

    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

Sources

  • CVE.orgVulnerability recordCVE-2026-66033

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-66033

    30-day exploitation probability 0.58%

    first.org
  • OpenSSF OSV / OSV ScannerPackage advisoryALPINE-CVE-2026-66033
    osv.dev
  • Trivy Vulnerability DBPackage advisoryALPINE-CVE-2026-66033

    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. A

    osv.dev

References

Freshness

Last verified in this catalog Oct 23, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.