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CVE details

CVE-2026-66035

libssh2 through 1.11.1, fixed in commit 42e33d8, contains a pre-authentication heap buffer overflow vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by sending a packet with a packet_length smaller than the cipher's block size during Encrypt-then-MAC cipher negotiation. In the fullpacket() function in src/transport.c, the ETM path allocates a buffer of packet_length bytes but copies blocksize minus one bytes via memcpy, causing an overflow that on 32-bit glibc writes attacker-controlled bytes into an adjacent chunk's SIZE field, enabling tcache bin confusion, overlapping live objects, and function pointer overwrite during the session handshake before authentication.

Score
7.7 high
Published
2026-07-24
Links
NVD · cve.org · Report wrong data

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 42e33d8, contains a
	pre-authentication heap buffer overflow vulnerability that allows a
	malicious SSH server to corrupt heap metadata in any connecting client
	by sending a packet with a packet_length smaller than the cipher's
	block size during Encrypt-then-MAC cipher negotiation. In the
	fullpacket() function in src/transport.c, the ETM path allocates a
	buffer of packet_length bytes but copies blocksize minus one bytes via
	memcpy, causing an overflow that on 32-bit glibc writes
	attacker-controlled bytes into an adjacent chunk's SIZE field,
	enabling tcache bin confusion, overlapping live objects, and function
	pointer overwrite during the session handshake before authentication.</p>
      </body>
    </description>
    <references>
      <cvename>CVE-2026-66035</cvename>
      <url>https://nvd.nist.gov/vuln/detail/CVE-2026-66035</url>
    </references>
    <dates>
      <discovery>2026-07-24</discovery>
      <entry>2026-10-26</entry>
    </dates>
  </vuln>