CVE-2025-32989: GNU GnuTLS Information Disclosure Flaw

CVE-2025-32989 Overview

A heap-buffer-overread vulnerability has been identified in GnuTLS affecting how the library handles the Certificate Transparency (CT) Signed Certificate Timestamp (SCT) extension during X.509 certificate parsing. This flaw allows a malicious user to craft a certificate containing a malformed SCT extension (OID 1.3.6.1.4.1.11129.2.4.2) that can lead to the exposure of sensitive data from memory. When GnuTLS verifies certificates from affected websites without properly validating the SCT extension, confidential information may be disclosed to attackers.

Critical Impact
This vulnerability enables information disclosure through improper certificate validation, potentially exposing sensitive data when GnuTLS processes maliciously crafted X.509 certificates with malformed SCT extensions.

Affected Products

GNU GnuTLS
Red Hat OpenShift Container Platform 4.0
Red Hat Enterprise Linux 6.0, 7.0, 8.0, 9.0, 10.0

Discovery Timeline

2025-07-10 - CVE-2025-32989 published to NVD
2025-12-01 - Last updated in NVD database

Technical Details for CVE-2025-32989

Vulnerability Analysis

The vulnerability resides in GnuTLS's X.509 certificate parsing functionality, specifically in the code path that processes the Certificate Transparency Signed Certificate Timestamp (SCT) extension. Certificate Transparency is a security mechanism designed to provide an open framework for monitoring and auditing TLS certificates. The SCT extension (identified by OID 1.3.6.1.4.1.11129.2.4.2) contains cryptographic proofs that a certificate has been logged to a public Certificate Transparency log.

When GnuTLS encounters a malformed SCT extension during certificate verification, insufficient bounds checking allows the parser to read beyond the allocated buffer boundaries. This heap-buffer-overread condition can result in the disclosure of adjacent memory contents, which may contain sensitive information such as cryptographic keys, session data, or other confidential application data.

Root Cause

The root cause is improper certificate validation (CWE-295) in the SCT extension parsing logic. The vulnerability stems from inadequate length validation when processing the SCT extension data structure. When a certificate contains a specially crafted SCT extension with manipulated length fields or malformed data, the parsing routine fails to properly verify that the declared data lengths match the actual buffer boundaries, leading to an out-of-bounds read condition.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can exploit this vulnerability by:

Creating a malicious X.509 certificate with a specially crafted SCT extension containing manipulated length fields
Deploying this certificate on a malicious server or through a man-in-the-middle position
When a client application using a vulnerable GnuTLS version attempts to verify the certificate, the heap-buffer-overread is triggered
Memory contents adjacent to the parsing buffer may be included in error responses or logging output, potentially disclosing sensitive information

The exploitation mechanism relies on the certificate verification process reading beyond buffer boundaries when parsing the malformed SCT extension data structure.

Detection Methods for CVE-2025-32989

Indicators of Compromise

Unusual TLS handshake failures or certificate verification errors in application logs
Memory access violations or segmentation faults in processes using GnuTLS
Unexpected data patterns in network traffic during TLS negotiation
Error messages referencing SCT extension parsing failures

Detection Strategies

Monitor application logs for GnuTLS certificate verification anomalies, particularly errors related to extension parsing
Deploy network intrusion detection signatures to identify certificates with abnormally sized SCT extensions
Utilize memory analysis tools to detect out-of-bounds read attempts in GnuTLS library operations
Implement certificate inspection at network boundaries to identify malformed X.509 certificates

Monitoring Recommendations

Enable verbose logging for TLS-related operations to capture certificate verification details
Configure alerting for repeated certificate verification failures from the same source
Monitor system memory usage for anomalies in processes that perform certificate validation
Review Certificate Transparency log interactions for suspicious certificate submissions

How to Mitigate CVE-2025-32989

Immediate Actions Required

Update GnuTLS to the latest patched version provided by your distribution
Apply Red Hat security advisories RHSA-2025:16115, RHSA-2025:16116, RHSA-2025:17181, RHSA-2025:17348, RHSA-2025:17361, RHSA-2025:19088, or RHSA-2025:22529 for affected Red Hat products
Audit systems for GnuTLS library usage and prioritize patching critical certificate validation services
Restart services that link against GnuTLS after applying patches to ensure the updated library is loaded

Patch Information

Red Hat has released multiple security advisories addressing this vulnerability across their product portfolio. For Red Hat Enterprise Linux versions 6.0 through 10.0 and OpenShift Container Platform 4.0, consult the Red Hat CVE Advisory for specific package versions and update instructions. The Red Hat Bug Report #2359621 contains additional technical details about the fix.

Workarounds

If immediate patching is not possible, consider implementing network-level certificate filtering to reject certificates with suspicious SCT extension characteristics
Limit exposure by restricting outbound connections from vulnerable systems to trusted certificate authorities only
Deploy additional monitoring on systems running vulnerable GnuTLS versions to detect potential exploitation attempts
Consider using alternative TLS libraries for critical applications until patching can be completed

bash

# Check installed GnuTLS version on RHEL/CentOS systems
rpm -qa | grep gnutls

# Update GnuTLS package on RHEL/CentOS
sudo dnf update gnutls

# Verify library version after update
gnutls-cli --version

# Restart services using GnuTLS (example: httpd)
sudo systemctl restart httpd