CVE-2026-58162: Apache Traffic Server SNI Vulnerability

CVE-2026-58162 Overview

CVE-2026-58162 affects the Apache Traffic Server certifier plugin. The plugin generates TLS certificates dynamically based on the Server Name Indication (SNI) value supplied by connecting clients. Because the SNI field is attacker-controlled and unvalidated, a remote client can force the server to issue certificates for arbitrary hostnames. This weakness is classified as improper certificate validation [CWE-295].

Affected releases include Apache Traffic Server versions 8.0.0 through 8.1.9, 9.0.0 through 9.2.14, and 10.0.0 through 10.1.3. The Apache Traffic Server project recommends upgrading to 9.2.15 or 10.1.4.

Critical Impact
Remote unauthenticated clients can trigger issuance of certificates for arbitrary hostnames, enabling downstream trust and impersonation abuse against services fronted by Traffic Server.

Affected Products

Apache Traffic Server 8.0.0 through 8.1.9
Apache Traffic Server 9.0.0 through 9.2.14
Apache Traffic Server 10.0.0 through 10.1.3

Discovery Timeline

2026-07-29 - CVE-2026-58162 published to NVD
2026-07-30 - Last updated in NVD database

Technical Details for CVE-2026-58162

Vulnerability Analysis

Apache Traffic Server ships an optional certifier plugin that dynamically generates leaf certificates for inbound TLS connections. The plugin derives the certificate subject and Subject Alternative Name (SAN) fields from the SNI extension in the client's ClientHello. The SNI value is client-supplied data and is not authenticated during the TLS handshake.

The plugin accepts this attacker-controlled hostname without validation against an allowlist or ownership check. As a result, a remote client can request a TLS session with any SNI value and cause the server to generate and cache a certificate matching that name. If the plugin's signing key is trusted downstream, the issued certificates carry the trust of that signing chain.

The root cause is improper certificate validation and hostname authorization [CWE-295] in the certifier plugin's certificate generation path.

Root Cause

The certifier plugin treats the client-provided SNI value as authoritative input for certificate generation. There is no check that the requester is entitled to a certificate for the requested name, and no restriction on which names the plugin will sign. Any hostname supplied in the TLS handshake becomes a valid certificate subject.

Attack Vector

Exploitation requires network reachability to a Traffic Server instance running the vulnerable certifier plugin. An attacker opens a TLS connection and sets the SNI extension to the target hostname (for example, an internal service or third-party domain). The plugin generates a certificate for that name using its signing key. The certificate can then be recovered by observing the server's presented chain and abused wherever the signing key is trusted.

Refer to the Apache Mailing List Discussion for the vendor's technical description.

Detection Methods for CVE-2026-58162

Indicators of Compromise

Unexpected certificate files in the certifier plugin's certificate cache directory that reference hostnames outside the organization's owned domains.
Traffic Server access logs showing TLS handshakes with anomalous or spoofed SNI values from untrusted client IP addresses.
Newly generated certificates signed by the plugin's certificate authority key that were not requested by legitimate operational workflows.

Detection Strategies

Audit the certifier plugin cache directory and compare issued certificate subjects against an allowlist of approved hostnames.
Monitor Traffic Server TLS handshake logs for high-cardinality or externally-controlled SNI values, especially from single source IPs.
Alert on the creation of certificates whose SAN or Common Name does not match domains under organizational control.

Monitoring Recommendations

Ingest Traffic Server access and error logs into a centralized analytics platform and build dashboards on SNI distribution over time.
Track the volume of certificates generated per hour by the certifier plugin and alert on statistical deviations from baseline.
Correlate TLS handshake events with downstream authentication or proxy failures that could indicate impersonation attempts.

How to Mitigate CVE-2026-58162

Immediate Actions Required

Upgrade Apache Traffic Server to version 9.2.15 or 10.1.4 on all affected deployments.
Rotate the signing key used by the certifier plugin and revoke any certificates issued during the exposure window.
Disable the certifier plugin on instances that do not require dynamic certificate generation until patching is complete.

Patch Information

The Apache Traffic Server project has released fixed versions 9.2.15 and 10.1.4. Users running the 8.x branch, which ended at 8.1.9, should migrate to a supported branch. Details are available in the Apache Mailing List Discussion.

Workarounds

Restrict which SNI values the certifier plugin will accept by configuring an explicit allowlist of permitted hostnames or domain suffixes.
Place Traffic Server behind a network control that filters TLS connections from untrusted sources before they reach the certifier plugin.
Isolate the plugin's signing key so it is not trusted by downstream clients or services outside its intended scope.

bash

# Verify Traffic Server version after upgrade
traffic_server -V

# Confirm the certifier plugin is loaded only where required
grep -i 'certifier.so' /etc/trafficserver/plugin.config