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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Connect to RSA-key-exchange TLS server
  2. Exploit
    Send abnormally short premaster secret
  3. Execution
    Trigger heap overread in libgnutls
  4. Impact
    Leak adjacent heap memory or crash service

Vulnerability Assessment

Weakness
CWE
CWE-1284
ASVS 5.0
V2 - Validation and Business Logic Input size validation
Exploitation Conditions

The server must be configured to perform RSA key exchange (legacy TLS_RSA_* cipher suites - not ephemeral/forward-secret (EC)DHE, and not TLS 1.3 which removes RSA key exchange), AND its RSA private key must be backed by a PKCS#11 token (e.g., an HSM, smartcard, or software token store) rather than held directly in software. Under those conditions the CVSS vector (AV:N/AC:L/PR:N/UI:N) indicates no authentication, no user interaction, and remote network reachability are required to send the malicious short premaster secret. Limiting factors that reduce real-world exposure: RSA key exchange is deprecated and disabled by default in many modern TLS stacks and entirely absent in TLS 1.3, and PKCS#11-backed keys are a specialized deployment choice - servers not meeting both prerequisites are not exploitable via this flaw.
Impact

The CVSS 3.1 vector (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H, base 8.2) describes a network-reachable, low-complexity attack requiring no privileges or user interaction, which on its face is high priority. However, two signals temper this: first, the impact profile shows only low confidentiality (C:L) with high availability impact (A:H), meaning the dominant real-world outcome is likely a crash/denial of service of the TLS service rather than large-scale data leakage, even though the description frames it as 'information disclosure' - these two sources are partly in tension and should be reconciled against the vendor advisory. Second, exploitation depends on a specific, increasingly uncommon configuration (RSA key exchange plus a PKCS#11-backed key), which sharply narrows the realistic attack surface despite the PR:N/AC:L scoring. There is no CISA KEV listing and no public exploit identified at time of analysis, so this is not confirmed actively exploited. EPSS and SSVC values were not supplied in the input, so probabilistic exploitation likelihood cannot be quoted here. Net assessment: a legitimate but configuration-gated issue - patch on affected Red Hat systems, but raw 8.2 likely overstates risk for the majority of deployments that do not use RSA key exchange with PKCS#11 tokens.
Exploit ScenarioDerived

An attacker who can reach a TLS server that still negotiates RSA key exchange and whose RSA private key is backed by a PKCS#11 token initiates a handshake and, instead of a normal-length encrypted premaster secret, supplies an extremely short one. GnuTLS reads past the allocated buffer, either crashing the service (high availability impact) or returning a small fragment of adjacent heap memory. No public proof-of-concept has been identified at time of analysis, but the attack requires no authentication or user interaction and is low-complexity for the narrow set of affected configurations.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.1% exploitation probability (EPSS)

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AnalysisAIv1 – May 26, 2026

Information disclosure and denial of service in GnuTLS (libgnutls) let a remote, unauthenticated attacker trigger a heap overread against TLS servers that perform legacy RSA key exchange using a private key backed by a PKCS#11 token. By sending an abnormally short premaster secret, the attacker causes the library to read beyond an allocated buffer (CWE-1284), which can leak a small amount of adjacent heap memory and, per the CVSS vector, more strongly impacts availability (A:H). No public exploit has been identified at time of analysis and the issue is not in CISA KEV; EPSS and SSVC data were not provided.

RemediationAI

No vendor-released patched version is identified in the provided data; the authoritative source for fixed package builds is the Red Hat advisory at https://access.redhat.com/security/cve/CVE-2026-5260 and Bugzilla 2467450 (https://bugzilla.redhat.com/show_bug.cgi?id=2467450) - apply the gnutls errata for your RHEL or OpenShift release once published and restart services linking libgnutls. As a compensating control until patched, disable static RSA key-exchange cipher suites and require forward-secret (EC)DHE suites or enforce TLS 1.3, which removes RSA key exchange entirely and eliminates the vulnerable code path; the trade-off is potential incompatibility with very old clients that only support RSA key exchange. Alternatively, where feasible, serve affected endpoints with private keys held in software rather than a PKCS#11 token to avoid the specific PKCS#11 decryption path, accepting the reduced key-protection guarantees that an HSM/token otherwise provides. Inventory which TLS-facing services actually combine RSA key exchange with PKCS#11-backed keys, since most modern configurations are not exposed.

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Technical ContextAI · show details

GnuTLS is a widely deployed open-source library implementing TLS/SSL, used by many Linux applications for secure transport. The flaw lies in the server-side handling of the RSA key-exchange handshake (the legacy TLS_RSA_* cipher suites, where the client encrypts a premaster secret under the server's RSA public key rather than using ephemeral Diffie-Hellman). When the server's RSA private key is offloaded to a PKCS#11 token - a cryptographic abstraction layer used for HSMs, smartcards, and software token stores - the code path that decrypts and processes the premaster secret fails to properly validate the supplied length. CWE-1284 (Improper Validation of Specified Quantity in Input) is the root cause: an attacker-controlled, extremely short premaster secret leads the library to read past the end of the buffer, a classic heap overread/memory-corruption condition.

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Severity by source

Vendor (redhat) PRIMARY 8.2 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
SUSE HIGH
Red Hat 8.2 MEDIUM

Primary rating from Vendor (redhat).

CVSS VectorVendor: redhat

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
High

DescriptionCVE.org

A flaw was found in libgnutls. A remote attacker, 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, could trigger a short heap overread. This memory corruption vulnerability could lead to information disclosure.

Executive ViewAI

Why It Matters

GnuTLS (libgnutls) contains a vulnerability enabling remote attackers without credentials to disrupt TLS services and leak sensitive data from servers using legacy RSA encryption with PKCS#11 tokens. The risk is concentrated in organizations deploying this older cryptographic configuration. No vendor patch is available.

Business Impact: High
Compensating Controls

Disable legacy RSA key exchange and enforce modern alternatives (ECDHE or DHE); implement strict connection rate limiting on TLS ports; apply network segmentation to restrict service exposure; enable connection logging to detect anomalies; use firewall rules to limit access to affected TLS endpoints. No vendor-released patch identified at time of analysis.

Threat Intelligence Overview

EPSS Score
0.1%
Top 66% exploitable
Social Media
1
Sightings
Data Quality
7 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment MSRC Vendor CIRCL VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity HIGH
CISA KEV No
Public POC No
EPSS 0.1%
Patch available Yes
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision
Scheduled
Exploitation
None
System Exposure· derived
Open
Automatable
Yes
Human Impact
High
Technical Impact
Partial

Priority Score

41
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +41
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Buffer Overflow HIGH

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

Affected Products (CPE)CVE.org

cpe:2.3:a:red_hat:red_hat_enterprise_linux_10:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_6:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_7:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_8:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_9:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_hardened_images:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_openshift_container_platform_4:*:*:*:*:*:*:*:*

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Same weakness CWE-1284 – Improper Validation of Specified Quantity in Input

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Vendor StatusVendor

SUSE

Severity: High
Product Status
Image SL-Micro-Azure Image SL-Micro-BYOS-Azure Image SL-Micro-BYOS-EC2 Image SL-Micro-BYOS-GCE Image SL-Micro-Base Image SL-Micro-Base-RT Image SL-Micro-Base-RT-SelfInstall Image SL-Micro-Base-RT-encrypted Image SL-Micro-Base-SelfInstall Image SL-Micro-Base-encrypted Image SL-Micro-Base-qcow Image SL-Micro-EC2 Image SLE-Micro Image SLE-Micro-Azure Image SLE-Micro-BYOS Image SLE-Micro-BYOS-Azure Image SLE-Micro-BYOS-EC2 Image SLE-Micro-BYOS-GCE Image SLE-Micro-EC2 Image SLE-Micro-GCE Image SUSE-Multi-Linux-Manager-Proxy-BYOS-Azure Image SUSE-Multi-Linux-Manager-Proxy-BYOS-EC2 Image SUSE-Multi-Linux-Manager-Proxy-BYOS-GCE Image SUSE-Multi-Linux-Manager-Server-Azure-llc Image SUSE-Multi-Linux-Manager-Server-Azure-ltd Image SUSE-Multi-Linux-Manager-Server-BYOS-Azure Image SUSE-Multi-Linux-Manager-Server-BYOS-EC2 Image SUSE-Multi-Linux-Manager-Server-BYOS-GCE Image SUSE-Multi-Linux-Manager-Server-EC2-llc Image SUSE-Multi-Linux-Manager-Server-EC2-ltd Affected
Image SLES-Azure-3P Image SLES-Azure-Basic Image SLES-Azure-Standard Image SLES-BYOS-Azure Image SLES-BYOS-EC2 Image SLES-BYOS-GCE Image SLES-EC2 Image SLES-GCE Image SLES-GCE-3P Image SLES-Hardened-BYOS-Azure Image SLES-Hardened-BYOS-EC2 Image SLES-Hardened-BYOS-GCE Image SLES-SAPCAL-Azure Image SLES-SAPCAL-EC2 Image SLES-SAPCAL-GCE Affected
Image SLES-SAP-Azure Image SLES-SAP-Azure-3P Image SLES-SAP-BYOS-Azure Image SLES-SAP-BYOS-EC2 Image SLES-SAP-BYOS-GCE Image SLES-SAP-EC2 Image SLES-SAP-GCE Image SLES-SAP-GCE-3P Affected
SUSE Liberty Linux 8 Fixed
SUSE Linux Enterprise Desktop 15 SP7 SUSE Linux Enterprise High Performance Computing 15 SP7 SUSE Linux Enterprise Module for Basesystem 15 SP7 SUSE Linux Enterprise Server 15 SP7 SUSE Linux Enterprise Server for SAP Applications 15 SP7 Fixed

References

Advisories & patches
ADVISORY https://ubuntu.com/security/notices/USN-8502-1 ADVISORY https://vuldb.com/vuln/365871 ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:2087/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:2115/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:21752/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:21784/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:21815/ REF https://access.redhat.com/errata/RHSA-2026:13274 REF https://access.redhat.com/errata/RHSA-2026:20611 REF https://access.redhat.com/errata/RHSA-2026:20612 REF https://access.redhat.com/errata/RHSA-2026:20613 REF https://access.redhat.com/errata/RHSA-2026:26319 REF https://access.redhat.com/errata/RHSA-2026:26409 REF https://access.redhat.com/errata/RHSA-2026:29197 REF https://access.redhat.com/errata/RHSA-2026:30004 REF https://access.redhat.com/errata/RHSA-2026:30849 REF https://access.redhat.com/errata/RHSA-2026:30850 REF https://access.redhat.com/errata/RHSA-2026:32962 REF https://access.redhat.com/errata/RHSA-2026:33125 REF https://access.redhat.com/errata/RHSA-2026:40762 REF https://access.redhat.com/errata/RHSA-2026:41921 REF https://access.redhat.com/errata/RHSA-2026:56853 REF https://access.redhat.com/errata/RHSA-2026:57483 REF https://access.redhat.com/errata/RHSA-2026:58981 REF https://access.redhat.com/errata/RHSA-2026:59831 REF https://access.redhat.com/errata/RHSA-2026:60019 REF https://access.redhat.com/errata/RHSA-2026:67837 REF https://access.redhat.com/errata/RHSA-2026:72502 REF https://access.redhat.com/errata/RHSA-2026:74674 REF https://access.redhat.com/errata/RHSA-2026:77320 REF https://access.redhat.com/errata/RHSA-2026:82304 REF https://access.redhat.com/errata/RHSA-2026:82322 REF https://access.redhat.com/errata/RHSA-2026:82347 REF https://access.redhat.com/errata/RHSA-2026:82354 REF https://access.redhat.com/errata/RHSA-2026:82372 REF https://access.redhat.com/errata/RHSA-2026:82857 REF https://access.redhat.com/errata/RHSA-2026:82888 REF https://access.redhat.com/security/cve/CVE-2026-5260 REF https://bugzilla.redhat.com/show_bug.cgi?id=2467450 REF https://www.gnutls.org/security-new.html#GNUTLS-SA-2026-04-29-10

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