Libgnutls — CraftedSignal Threat Feedhttps://feed.craftedsignal.io/products/libgnutls/Trending threats, MITRE ATT&CK coverage, and detection metadata. Fed continuously.Hugoenhello@craftedsignal.iohello@craftedsignal.ioTue, 26 May 2026 22:19:06 +0000CVE-2026-5260: libgnutls Heap Overread via Short Premaster Secrethttps://feed.craftedsignal.io/briefs/2026-05-cve-2026-5260-gnutls-heap-overread/Tue, 26 May 2026 22:19:06 +0000hello@craftedsignal.iohttps://feed.craftedsignal.io/briefs/2026-05-cve-2026-5260-gnutls-heap-overread/A remote attacker can trigger a heap overread in libgnutls by sending an extremely short premaster secret during an RSA key exchange to a server using an RSA key backed by a PKCS#11 token, potentially leading to information disclosure.CVE-2026-5260 describes a heap overread vulnerability found in libgnutls. The vulnerability arises during RSA key exchange when a server uses an RSA key backed by a PKCS#11 token. An attacker can exploit this flaw by sending an extremely short premaster secret. This leads to a short heap overread, a type of memory corruption vulnerability. Successful exploitation could result in the disclosure of sensitive information. This vulnerability impacts systems using vulnerable versions of libgnutls and could potentially affect any application or service relying on the library for secure communication.

Attack Chain

  1. Attacker initiates an RSA key exchange with a server using a libgnutls implementation.
  2. The server’s RSA key is backed by a PKCS#11 token for cryptographic operations.
  3. Attacker sends a crafted TLS ClientHello message to initiate the handshake.
  4. The attacker provides an extremely short premaster secret in the ClientKeyExchange message.
  5. libgnutls processes the short premaster secret during the RSA decryption process.
  6. Due to insufficient bounds checking, the processing of the short premaster secret triggers a heap overread.
  7. The heap overread allows the attacker to potentially read beyond the allocated memory buffer.
  8. Sensitive information is disclosed, potentially compromising the confidentiality of the communication.

Impact

Successful exploitation of CVE-2026-5260 can lead to information disclosure. Specifically, an attacker could potentially read sensitive data stored in memory adjacent to the overread buffer. The impact is limited to information disclosure, but the sensitivity of the disclosed data depends on the context and the application using libgnutls. The number of potential victims is broad, as many applications rely on libgnutls for TLS/SSL functionality.

Recommendation

  • Upgrade to the latest version of libgnutls that contains the fix for CVE-2026-5260.
  • Deploy the Sigma rules provided in this brief to your SIEM to detect potential exploitation attempts.
  • Monitor network traffic for anomalous TLS handshake patterns involving short premaster secrets using network connection logs.
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