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CVE details

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. 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.

Score
8.7 high
Published
2026-07-24
Links
NVD · cve.org

Matched ports (2)

PortPackageVersionStatusMaintainer
security/libssh2libssh21.11.1_1,3unaddressedsbz@FreeBSD.org
security/linux-c7-libssh2linux-c7-libssh21.8.0_2unaddressedemulation@FreeBSD.org

Template for a VuXML entry

Range taken from the CVE record, check it before committing. make newentry in security/vuxml creates the vid.

  <vuln vid="FIXME (make newentry)">
    <topic>FIXME -- FIXME</topic>
    <affects>
      <package>
	<name>libssh2</name>
	<range><lt>FIXME</lt></range>
      </package>
      <package>
	<name>linux-c7-libssh2</name>
	<range><lt>FIXME</lt></range>
      </package>
    </affects>
    <description>
      <body xmlns="http://www.w3.org/1999/xhtml">
	<p>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.</p>
      </body>
    </description>
    <references>
      <cvename>CVE-2026-66033</cvename>
      <url>https://nvd.nist.gov/vuln/detail/CVE-2026-66033</url>
    </references>
    <dates>
      <discovery>2026-07-24</discovery>
      <entry>2026-10-26</entry>
    </dates>
  </vuln>