Red Hat Enterprise Linux 10 CVE-2026-42013

{
  "product_name": "GnuTLS",
  "summary": "Certificate validation bypass in GnuTLS (as shipped in Red Hat Enterprise Linux 6 through 10, OpenShift Container Platform 4, and Red Hat Hardened Images) lets a remote attacker defeat hostname verification: when a certificate carries an oversized Subject Alternative Name, the library incorrectly abandons SAN matching and falls back to the legacy Common Name field, accepting certificates it should reject. An attacker positioned to intercept traffic can present such a certificate to impersonate a trusted server and conduct spoofing or man-in-the-middle attacks against TLS clients that rely on GnuTLS. There is no public exploit identified at time of analysis, no CISA KEV listing, and no EPSS score in the provided data.",
  "technical_context": "GnuTLS is a widely deployed open-source implementation of TLS/SSL and related cryptographic protocols, used by countless Linux applications for establishing authenticated, encrypted connections. During X.509 certificate verification, modern practice requires that the presented hostname be matched against the Subject Alternative Name (SAN) extension, with the deprecated Common Name (CN) field used only as a legacy fallback. The flaw is classified as CWE-1284 (Improper Validation of Specified Quantity in Input): an oversized SAN value is not handled correctly during length/quantity validation, causing the verification routine to skip proper SAN matching and revert to the weaker CN check. Because the CN field is attacker-influenceable and not bound to the same constraints, this fallback effectively neutralizes the protection SAN matching is supposed to provide. The affected packages span Red Hat Enterprise Linux 6, 7, 8, 9, and 10, OpenShift Container Platform 4, and Red Hat Hardened Images, per the supplied CPE data.",
  "risk_assessment": "Signals are mixed and incomplete. The CVSS 3.1 base score of 8.2 with vector AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N reflects an unauthenticated, low-complexity, network-reachable issue with high integrity impact (authentication/trust bypass) and only low confidentiality impact, no availability impact. However, the CVSS network/no-privilege rating understates a practical precondition: to weaponize a certificate-validation bypass an attacker generally needs a man-in-the-middle or interception position, which CVSS does not model as a privilege, so verify realistic exposure against your network topology rather than treating it as trivially remote. No EPSS score, no SSVC decision data, and no KEV status were provided, so exploitation probability cannot be quantified from the input. There is no public exploit identified at time of analysis. Net assessment: a genuinely serious trust-bypass weakness in a foundational TLS library warranting prompt patching, but absent KEV/EPSS/POC evidence it currently reads as a high-severity hygiene fix rather than an actively-exploited emergency.",
  "affected_products": "The flaw affects the GnuTLS library as distributed by Red Hat across Red Hat Enterprise Linux 6, 7, 8, 9, and 10 (cpe:2.3:a:red_hat:red_hat_enterprise_linux_6 through _10), Red Hat OpenShift Container Platform 4 (cpe:2.3:a:red_hat:red_hat_openshift_container_platform_4), and Red Hat Hardened Images (cpe:2.3:a:red_hat:red_hat_hardened_images). Specific fixed package versions are not enumerated in the provided data; the input references only Red Hat tracking resources rather than tagged releases. Consult the Red Hat advisory at https://access.redhat.com/security/cve/CVE-2026-42013 and the tracking bug at https://bugzilla.redhat.com/show_bug.cgi?id=2467448 for per-product errata and exact patched build numbers.",
  "remediation": "No vendor-released patch version is identified in the provided data, although Red Hat is tracking the issue; monitor https://access.redhat.com/security/cve/CVE-2026-42013 and apply the GnuTLS errata for your specific RHEL or OpenShift stream as soon as Red Hat publishes fixed package builds, then restart or redeploy all services that link GnuTLS so the corrected library is loaded. As a compensating control until errata are available, reduce reliance on GnuTLS-based trust decisions for high-value connections: pin expected server certificates or public keys in clients you control, require mutual TLS so the server is not the only authenticated party, and restrict outbound TLS to known endpoints so an interception position is harder to obtain. Each of these has trade-offs: certificate/key pinning increases operational overhead during legitimate certificate rotation, mutual TLS requires client-certificate provisioning, and egress restriction can break legitimate connections to new endpoints, so validate them in staging before broad rollout. Track fixed versions at https://bugzilla.redhat.com/show_bug.cgi?id=2467448 and update this remediation once exact patched builds are confirmed; do not assume the absence of a listed version means no fix is forthcoming.",
  "exploit_scenario": "An attacker who can intercept a victim's TLS traffic (for example on a shared or compromised network segment, or via DNS/ARP redirection) presents a certificate crafted with an oversized SAN entry. GnuTLS aborts proper SAN matching and falls back to the CN field, which the attacker has populated with the target hostname, so the spoofed certificate is accepted and the attacker transparently relays or modifies the now-trusted session. No public exploit code is identified at time of analysis, and the low attack complexity (AC:L) means crafting the malicious certificate is straightforward once an interception position exists.",
  "exploitation_conditions": "Exploitation requires two concrete elements drawn from the description and CVSS vector. First, the attacker must supply an X.509 certificate containing an oversized Subject Alternative Name value that triggers GnuTLS's incorrect fallback from SAN matching to Common Name matching, with the target hostname placed in the CN field. Second, the attacker must occupy a position to deliver that certificate to a GnuTLS-based client during connection setup, i.e., a man-in-the-middle or traffic-interception capability, since the bypass only yields value when impersonating a legitimate endpoint. The CVSS vector confirms no authentication (PR:N) and no user interaction (UI:N) are needed against the library itself and the attack is network-reachable (AV:N) with low complexity (AC:L). Limiting factors: the victim application must use GnuTLS for certificate verification and must perform hostname validation, the attacker needs the interception position to be useful, and impact is integrity/trust (I:H) rather than direct data disclosure (C:L) or denial of service (A:N).",
  "attack_chain": "Gain traffic interception position → Present certificate with oversized SAN → Trigger GnuTLS fallback to CN check → Spoofed certificate validated against CN → Relay or modify trusted TLS session",
  "confidence_notes": "Affected product scope (RHEL 6-10, OpenShift Container Platform 4, Red Hat Hardened Images), the CWE-1284 root-cause class, and the CVSS 3.1 vector are confirmed from Red Hat-supplied input. The man-in-the-middle precondition is inferred from the description and the nature of certificate-validation bypasses, not stated verbatim. Exact patched package versions, EPSS score, SSVC data, KEV status, and any POC are not present in the provided data; there is no public exploit identified at time of analysis, and fixed versions should be confirmed against the Red Hat advisory and Bugzilla before remediation is closed out."
}