Description

A security flaw has been discovered in mwiede jsch up to 2.28.5. Affected is the function getRevokedKeys of the file src/main/java/com/jcraft/jsch/KnownHosts.java. Performing a manipulation of the argument known_hosts results in improper check for certificate revocation. The attack is possible to be carried out remotely. The attack is considered to have high complexity. The exploitability is told to be difficult. The exploit has been released to the public and may be used for attacks. Upgrading to version 2.28.6 is able to address this issue. The patch is named 194a2f76a5c0f1c3f778565be3fd66bcafc42d23. You should upgrade the affected component.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "3.7",
  "pubDate": "2026-09-06T23:17:39.157Z",
  "pubdate": "2026-09-06T23:17:39.157Z",
  "executiveSummary": "A security vulnerability has been identified in the mwiede jsch library, affecting versions up to 2.28.5. The vulnerability manifests as an improper check for certificate revocation within the getRevokedKeys function located in src/main/java/com/jcraft/jsch/KnownHosts.java.\nThis flaw allows a remote attacker to circumvent certificate revocation protections by manipulating the known_hosts argument. Successful exploitation could lead to the acceptance of revoked SSH host keys, undermining the cryptographic integrity of the connection.\nAlthough the attack is classified as having high complexity and difficult exploitability, its remote nature and the public availability of an exploit increase the overall risk. Organizations relying on this library for secure shell communications are at risk of man-in-the-middle or impersonation attacks if they do not address this implementation flaw.\nThe vulnerability is resolved by updating the affected component to version 2.28.6, which incorporates the necessary patch identified by commit 194a2f76a5c0f1c3f778565be3fd66bcafc42d23.",
  "technicalDetails": "The vulnerability resides in the getRevokedKeys function within the KnownHosts.java file of the mwiede jsch library. The root cause is a logic flaw in how the library processes and validates revoked keys against the provided known_hosts file.\nWhen a connection is established, the library is expected to consult the known_hosts file to verify the validity of the server's public key. The getRevokedKeys method is intended to identify whether a given key or certificate has been explicitly revoked by the administrator or via protocol-defined revocation mechanisms.\nDue to improper input validation and conditional logic processing during the evaluation of the known_hosts argument, the function fails to correctly identify or enforce the revoked status of a certificate. An attacker capable of manipulating the known_hosts input or controlling the server-side key presentation can exploit this weakness.\nThe attack flow involves the following steps: First, an attacker intercepts or impersonates a legitimate SSH server, presenting a compromised or previously revoked public key. Second, the client library invokes the getRevokedKeys function to verify the status of the presented credential. Third, due to the faulty validation logic, the function fails to correctly match the presented key against the revocation criteria defined within the local known_hosts file. Fourth, the library proceeds to trust the revoked key, effectively bypassing the revocation check.\nThis allows the attacker to maintain a persistent connection or perform unauthorized operations while appearing to be a trusted host. The exploitation is performed remotely and does not require local system access; however, the high complexity and difficulty of exploitation suggest it requires specific environmental configurations or precise timing regarding the interaction with the known_hosts file. The impact is significant, as it effectively renders the revocation check mechanism inert, allowing for the potential usage of blacklisted credentials in authenticated sessions.\nThe affected versions include all mwiede jsch releases up to 2.28.5. The issue is officially remediated in version 2.28.6, which updates the logic in KnownHosts.java to ensure that revocation lists are processed with the required precision, ensuring that any revoked key encountered is correctly rejected by the client."
}