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Advisories

libssh2 Integer Underflow DoS via AES-GCM Cipher Negotiation

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severity
high
date
Affecting

  • libssh2 <= 1.11.1, fixed in commit a2ed82d

CWE
  • CWE-191 Integer Underflow (Wrap or Wraparound)
  • CWE-125 Out-of-bounds Read
CVSS
8.7
CVSS V4 Vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Credit
VladimirEliTokarev
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.

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