Listen to this Post
The vulnerability occurs in libssh when utilizing the ChaCha20 cipher through OpenSSL. During cipher context initialization, if heap memory is exhausted, OpenSSL returns an error code. Due to a misalignment in error code mapping, this OpenSSL error aliases with libssh’s SSH_OK code. Consequently, libssh fails to detect the error and proceeds with a partially initialized cipher context. This incomplete initialization leads to undefined behavior during cryptographic operations. Specifically, encryption and decryption may use uninitialized or incorrect state, compromising data confidentiality. Attackers can exploit this by inducing heap exhaustion, possibly through crafted requests or resource consumption. The flaw is inherent in the error handling logic between libssh and OpenSSL. When ChaCha20 is selected, libssh calls OpenSSL’s EVP_EncryptInit_ex or similar functions. On heap failure, OpenSSL might return 0, which libssh interprets as SSH_OK. This causes libssh to skip error checks and use the cipher context. The partially initialized context can result in plaintext leakage or ciphertext corruption. Additionally, crashes may occur due to invalid memory access. The vulnerability requires specific conditions: ChaCha20 cipher usage and heap exhaustion. It affects both client and server implementations using libssh with OpenSSL. Mitigation involves proper error handling and memory management. Patches should ensure that OpenSSL errors are correctly propagated and handled in libssh.
Platform: libssh
Version: multiple versions
Vulnerability: Cipher context flaw
Severity: Critical
Date: 2025-07-07
Prediction: Patch expected 2025-08-01
What Undercode Say:
Analytics:
Showing bash commands and codes related to the blog
`ssh -Q cipher | grep chacha`
`ldd $(which sshd) | grep libssh`
`valgrind –leak-check=full ssh -c [email protected]`
Exploit:
Exhaust heap memory.
Initiate ChaCha20 connections.
Corrupt cryptographic operations.
Protection from this CVE:
Update libssh version.
Disable ChaCha20 cipher.
Monitor memory usage.
Impact:
Data confidentiality compromised.
Data integrity risk.
Application crashes possible.
🎯Let’s Practice Exploiting & Learn Patching For Free:
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
Undercode
