CVE-2026-59847 in Red Hat
Summary
by MITRE • 07/21/2026
A flaw was found 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.
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Analysis
by VulDB Data Team • 07/21/2026
This vulnerability resides within the libssh library's implementation of the Advanced Encryption Standard with Galois/Counter Mode authentication, specifically affecting builds that utilize the OpenSSL backend for cryptographic operations. The flaw manifests in the improper finalization checks during the AES-GCM encryption process, which fundamentally undermines the integrity protection mechanisms that should safeguard data transmitted over secure channels. When these finalization checks fail to properly validate the authentication tags generated during encryption, an attacker positioned within the network path can manipulate plaintext data without triggering any detection mechanisms, effectively bypassing the cryptographic integrity controls that are essential for maintaining secure communications.
The technical nature of this vulnerability aligns with CWE-310, which addresses Cryptographic Issues related to improper implementation of cryptographic algorithms. The flaw represents a critical weakness in the authentication mechanism where the GCM mode's tag verification process becomes ineffective, allowing attackers to perform man-in-the-middle modifications to transmitted data. This type of vulnerability falls under ATT&CK technique T1566.002 which covers Phishing with Malicious Attachments or Links, but more specifically relates to T1071.004 for Application Layer Protocol: SSH, as it compromises the integrity of secure shell communications. The vulnerability's impact extends beyond simple data modification since it fundamentally breaks the cryptographic assurances that users expect when establishing secure connections through SSH protocols.
The operational consequences of this vulnerability are severe for any system relying on libssh for secure communications, particularly in environments where network traffic may be subject to interception or manipulation by adversaries. Attackers can exploit this weakness to modify sensitive data in transit without detection, potentially leading to unauthorized access, data corruption, or the introduction of malicious content into established sessions. Systems using affected versions of libssh are vulnerable regardless of whether they are acting as servers or clients, making the attack surface particularly broad across network infrastructure and applications that depend on SSH for secure communication channels. The vulnerability is especially concerning in enterprise environments where SSH is commonly used for remote administration, automated deployments, and secure data transfer operations.
Mitigation strategies should focus on immediate patching of affected libssh installations to address the cryptographic implementation flaw in AES-GCM finalization checks. Organizations must also implement network monitoring solutions capable of detecting anomalous traffic patterns that might indicate exploitation attempts, particularly when dealing with SSH communications. Additionally, system administrators should consider implementing alternative encryption mechanisms or strengthening overall network security controls through traffic inspection and anomaly detection systems. The remediation process should include comprehensive testing to ensure that patched versions maintain proper cryptographic functionality while not introducing regressions in existing SSH operations. Organizations should also conduct thorough vulnerability assessments across their entire infrastructure to identify all systems using affected libssh versions, as this vulnerability may be present in various applications and services that depend on the library for secure communications.