CVE-2026-14457: OpenSSL RPK Configuration DOS Vulnerability

CVE-2026-14457 Overview

CVE-2026-14457 is a NULL pointer dereference vulnerability in OpenSSL affecting TLS deployments that use RFC7250 Raw Public Keys (RPKs). The flaw triggers when a peer configures only a private key with no associated certificate, and the remote peer solicits raw public keys while also sending the signature_algorithms_cert TLS extension. Processing the extension without a certificate context causes the application to abort. The vulnerability is classified as [CWE-476: NULL Pointer Dereference]. Impact is limited to denial of service; no data disclosure or code execution is possible. FIPS modules are not affected, as the SSL protocol implementation is outside the OpenSSL FIPS module boundary.

Critical Impact
Remote unauthenticated attackers can crash OpenSSL-based TLS servers or clients configured with RPK-only (no certificate) private keys by sending a crafted signature_algorithms_cert extension.

Affected Products

OpenSSL deployments with RFC7250 Raw Public Keys enabled
Server or client configurations using a private key with no associated certificate
Applications relying on OpenSSL's TLS 1.3 implementation for RPK negotiation

Discovery Timeline

2026-08-25 - CVE-2026-14457 published to NVD
2026-08-25 - OpenSSL security advisory released
2026-08-25 - Last updated in NVD database

Technical Details for CVE-2026-14457

Vulnerability Analysis

The vulnerability resides in OpenSSL's TLS extension handling logic in ssl/t1_lib.c. When RFC7250 Raw Public Keys are enabled, OpenSSL allows a peer to authenticate using only a bare public key rather than a full X.509 certificate. The signature_algorithms_cert extension, defined in TLS 1.3, constrains the signature algorithms acceptable on certificates within a chain. In a key-only RPK deployment, no certificate exists to constrain, but the extension-processing code does not account for this state and attempts to dereference a NULL certificate structure.

The result is an application abort producing a denial of service on the affected endpoint. An unauthenticated network attacker can trigger the condition by initiating a TLS handshake that solicits raw public keys and includes the typically omitted signature_algorithms_cert extension.

Root Cause

Documentation samples suggested key-only RPK configurations were supported, but the extension-processing path assumed a certificate would always be present. When x == NULL and the negotiated certificate type is not RPK, the code dereferences the missing certificate object. The fix short-circuits the check when RPK is negotiated and returns failure when a key-only slot is not usable.

Attack Vector

Exploitation requires network access to a TLS endpoint that has RPK enabled and is configured with a private key but no certificate. The attacker initiates a TLS handshake advertising RPK support and includes the signature_algorithms_cert extension. No authentication or user interaction is required.

     if (supported <= 0)
         return 0;
 
+    /*
+     * When RPK is negotiated there are no certificate signatures to
+     * constrain, and there may not even be a certificate configured.
+     */
+    if (TLSEXT_cert_type_rpk == (s->server ? s->ext.server_cert_type : s->ext.client_cert_type))
+        return 1;
+
+    /*
+     * RPK was enabled, adding candidate private-key-only slots, but was not
+     * negotiated, so the key-only slot is not usable.
+     */
+    if (x == NULL)
+        return 0;
+
     /*
      * The TLS 1.3 signature_algorithms_cert extension places restrictions
      * on the sigalg with which the certificate was signed (by its issuer).

Source: OpenSSL Commit Fix

Detection Methods for CVE-2026-14457

Indicators of Compromise

Unexpected termination or SIGSEGV crashes of TLS server or client processes linked against vulnerable OpenSSL versions.
TLS handshake logs showing client_hello or server_hello messages containing server_certificate_type=RawPublicKey combined with the signature_algorithms_cert extension.
Repeated inbound TLS handshake attempts from the same source preceding service restarts.

Detection Strategies

Inspect TLS handshake telemetry for the combination of RFC7250 RPK negotiation and the signature_algorithms_cert extension, which is atypical in RPK-only deployments.
Correlate application crash dumps with OpenSSL stack frames in tls_choose_sigalg or signature_algorithms_cert extension parsing.
Audit deployed OpenSSL binaries and libraries to identify versions predating the fix commits referenced in the OpenSSL advisory.

Monitoring Recommendations

Monitor process supervision logs (systemd, container orchestrators) for abnormal restart frequency of TLS-terminating services.
Enable core dump collection on TLS-facing services to capture crash context for triage.
Track TLS handshake failure rates as a leading indicator of exploitation attempts against RPK-enabled endpoints.

How to Mitigate CVE-2026-14457

Immediate Actions Required

Upgrade to the fixed OpenSSL release identified in the OpenSSL Security Advisory.
Inventory all applications and services using OpenSSL with RFC7250 Raw Public Keys enabled.
Restart TLS-terminating services after patching to ensure the updated library is loaded.

Patch Information

The OpenSSL project addressed the issue across multiple branches. Review the upstream commits: 1e8c398d, 581aaa0f, d0af2047, and dad836b0. The fix ensures the signature_algorithms_cert extension check returns early when RPK is negotiated and rejects the key-only slot when RPK was enabled but not negotiated.

Workarounds

Configure a matching certificate alongside the private key, even a self-signed certificate, which handles the signature_algorithms_cert extension reliably without the fix.
Disable RFC7250 Raw Public Key support on TLS servers and clients until patching is complete.
Restrict network exposure of RPK-enabled endpoints to authenticated peers where feasible.

bash

# Verify installed OpenSSL version
openssl version -a

# Example: configure a self-signed certificate to accompany the private key
openssl req -x509 -new -nodes -key private.key -sha256 -days 365 -out server.crt -subj "/CN=rpk-endpoint"