CVE-2025-5987
HighCVSS 8.1Exploitation Probability (EPSS)
High risk77th percentile - higher than 77% of all known CVEs
Summary
A flaw was found in libssh when using the ChaCha20 cipher with the OpenSSL library. If an attacker exhausts the heap space, the error is not detected and may lead to libssh using a partially initialized cipher context. This occurs because the OpenSSL error code aliases with SSH_OK, preventing proper error detection.
Risk Assessment
This vulnerability can lead to undefined behavior, including compromised data confidentiality and integrity or system crashes, posing a significant security risk to the organization.
Recommendation
Immediately update libssh to a version that fixes the OpenSSL error handling for the ChaCha20 cipher. Until updated, avoid using the ChaCha20 cipher with OpenSSL.
Other vulnerabilities in libssh
See all- CVE-2026-3731Medium
In libssh up to 0.11.3, the functions sftp_extensions_get_name and sftp_extensions_get_data in src/sftp.c (SFTP Extension Name Handler component) can cause an out-of-bounds read when the idx argument is manipulated. The attack may be performed remotely. Upgrading to version 0.11.4 or 0.12.0 resolves the issue (patch 855a0853ad3abd4a6cd85ce06fce6d8d4c7a0b60).
- CVE-2023-1667Medium
A NULL pointer dereference was found in libssh during re-keying with algorithm guessing. This issue may allow an authenticated client to cause a denial of service.
- CVE-2015-3146High
Versions of libssh before 0.6.5 have a state validation issue in the handling of SSH_MSG_NEWKEYS and SSH_MSG_KEXDH_REPLY packets, which can lead to system crashes.
- CVE-2026-59851High
Vulnerability in the libssh library on servers with GSSAPIKeyExchange enabled. The gssapi-keyex path does not verify whether the authenticated Kerberos principal is authorized for the requested local user, allowing authenticated clients to log in as arbitrary users.
- CVE-2026-59850Medium
In the libssh library, if data packets are processed after a channel is closed, channel data callbacks can be invoked after the associated data has already been freed, leading to crashes or possible use-after-free conditions.
- CVE-2026-59849Low
A logic error in libssh's automatic certificate-based public key authentication causes libssh clients to loop indefinitely when configured certificates are missing or repeatedly rejected by a server, leading to denial of service.
- CVE-2026-59848Medium
Vulnerability in libssh. A malicious SFTP server can send responses for unknown request IDs, causing unbounded memory growth and client-side denial of service.
- CVE-2026-59847Medium
A flaw in libssh. Incorrect AES-GCM finalization checks in builds using the OpenSSL backend can effectively remove integrity protection, allowing an in-path attacker to modify plaintext on the wire without detection.
- CVE-2026-59846Low
A flaw in libssh: a malicious username expanded through %r in ProxyCommand handling can inject shell metacharacters, exposing environment variables and causing unintended shell behavior.
- CVE-2026-59845Medium
In libssh, when ProxyCommand is used, an unchecked fork() failure can result in storing PID -1. During cleanup, signals may be sent to processes in the caller's process tree, causing local denial of service.
Original NVD description (English source)
A flaw was found in libssh when using the ChaCha20 cipher with the OpenSSL library. If an attacker manages to exhaust the heap space, this error is not detected and may lead to libssh using a partially initialized cipher context. This occurs because the OpenSSL error code returned aliases with the SSH_OK code, resulting in libssh not properly detecting the error returned by the OpenSSL library. This issue can lead to undefined behavior, including compromised data confidentiality and integrity or crashes.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS