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CVE-2026-5260 Red Hat CVE debrief

A memory corruption vulnerability in libgnutls allows remote attackers to trigger a short heap overread during RSA key exchange when an extremely short premaster secret is sent to a server using an RSA key backed by a PKCS#11 token. The vulnerability, published on 2026-05-26, stems from improper handling of undersized premaster secrets in the RSA key exchange implementation. Successful exploitation could lead to information disclosure through the heap overread. The attack vector is network-based with low attack complexity, requiring no privileges or user interaction. The vulnerability is classified under CWE-1284 (Improper Validation of Specified Quantity in Input).

Vendor
Red Hat
Product
Red Hat Enterprise Linux 8
CVSS
HIGH 8.2
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-26
Original CVE updated
2026-05-27
Advisory published
2026-05-26
Advisory updated
2026-05-27

Who should care

Organizations operating TLS servers with RSA certificates where private keys are stored in PKCS#11 tokens, HSMs, or smart cards; financial services and government entities using hardware-backed cryptographic key storage; cloud providers offering managed TLS termination with HSM integration; security teams responsible for TLS/SSL infrastructure and cryptographic library maintenance

Technical summary

The vulnerability exists in libgnutls' handling of RSA key exchange when the server uses an RSA private key backed by a PKCS#11 cryptographic token. During the TLS handshake, when a client sends an RSA-encrypted premaster secret, the server decrypts this value using the PKCS#11 token. If an attacker sends an extremely short premaster secret, the implementation fails to properly validate the decrypted length before memory operations, resulting in a short heap overread. This memory corruption can expose sensitive heap contents to the attacker. The vulnerability is particularly relevant for deployments using hardware security modules (HSMs) or smart cards via PKCS#11 for key protection, as these configurations trigger the affected code path. The CVSS 3.1 score of 8.2 reflects high availability impact combined with low confidentiality impact, indicating potential for denial of service alongside information disclosure.

Defensive priority

HIGH

Recommended defensive actions

  • Upgrade libgnutls to a patched version when available from your distribution vendor
  • Monitor Red Hat security advisories for specific patch availability and deployment guidance
  • Review TLS server configurations using RSA keys backed by PKCS#11 tokens for exposure
  • Apply network segmentation controls to limit exposure of TLS termination endpoints using PKCS#11-backed keys
  • Enable TLS session logging to detect anomalous RSA key exchange patterns that may indicate exploitation attempts
  • Validate that HSM/PKCS#11 token integrations enforce minimum premaster secret length requirements

Evidence notes

Official CVE record and NVD entry published 2026-05-26. Red Hat security advisory and Bugzilla tracking bug confirm vendor awareness. CVSS 3.1 vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H.

Official resources

2026-05-26