CVE-2026-58164: Apache Traffic Server Use-After-Free Flaw

CVE-2026-58164 Overview

CVE-2026-58164 affects Apache Traffic Server (ATS), an open-source caching proxy and reverse proxy used at internet scale. The vulnerability combines a use-after-free flaw [CWE-416] with a time-of-check to time-of-use (TOCTOU) race condition in the handling of remap configuration. Attackers can trigger the flaws remotely over the network without authentication, targeting availability of the proxy service. The issue affects 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 has released fixed versions 9.2.15 and 10.1.4.

Critical Impact
Remote, unauthenticated attackers can exploit memory corruption and a race condition in remap configuration handling to disrupt Apache Traffic Server availability.

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-2026-58164 published to NVD
2026-07-30 - Last updated in NVD database

Technical Details for CVE-2026-58164

Vulnerability Analysis

Apache Traffic Server processes remap rules that map incoming request URLs to upstream origins. The remap configuration subsystem contains two related defects. The first is a use-after-free condition [CWE-416] where a freed remap object or associated memory is referenced after deallocation. The second is a time-of-check to time-of-use race, where the state of remap configuration data changes between validation and use. Both defects reside in the remap configuration handling path, which is reachable through normal proxy request processing.

Exploitation targets availability, with a lower impact on confidentiality and integrity. A successful trigger can crash the ATS worker process or cause undefined behavior in request routing. Because ATS commonly sits at the edge of high-throughput environments, an outage of the proxy tier interrupts downstream services.

Root Cause

The root cause is unsafe lifecycle management of remap configuration objects. Reference counting or locking around remap rules does not fully protect against concurrent access during configuration reload or lookup. When one execution path frees a remap structure while another still holds a pointer to it, subsequent dereferences read or write freed memory. The TOCTOU component compounds this by allowing configuration state to shift between the validation check and the operation that consumes it.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker sends crafted HTTP requests that traverse the remap subsystem, potentially in combination with events that trigger remap reloads or lookups. The race window and the freed-object dereference can be induced through repeated requests. No public exploit is currently referenced in the advisory. See the Apache Mailing List Thread for the project announcement.

Detection Methods for CVE-2026-58164

Indicators of Compromise

Unexpected crashes or restarts of the traffic_server process, particularly during or shortly after remap configuration reloads.
Core dumps or ASAN-style errors referencing remap rule structures in RemapConfig or UrlRewrite code paths.
Bursts of malformed or unusual HTTP requests preceding proxy instability in diags.log or error.log.

Detection Strategies

Monitor Apache Traffic Server version banners and package inventories to identify hosts running affected releases 8.0.0–8.1.9, 9.0.0–9.2.14, or 10.0.0–10.1.3.
Alert on abnormal termination of ATS worker processes and correlate with recent request patterns.
Track configuration reload events (traffic_ctl config reload) alongside request logs to spot exploitation attempts targeting the race window.

Monitoring Recommendations

Ingest ATS access, error, and diagnostic logs into a centralized analytics platform for correlation with process crash telemetry.
Enable process-level monitoring on ATS hosts to detect segmentation faults and abnormal exits.
Baseline normal remap reload frequency and alert on unusual reload activity from management interfaces.

How to Mitigate CVE-2026-58164

Immediate Actions Required

Upgrade Apache Traffic Server to version 9.2.15 or 10.1.4 as recommended by the Apache Software Foundation.
Inventory all ATS deployments and identify instances running any 8.x, 9.x, or 10.x release below the fixed versions.
Restrict network exposure of ATS management endpoints and limit inbound traffic to trusted sources where feasible.

Patch Information

Apache Traffic Server versions 9.2.15 and 10.1.4 contain the fixes for the use-after-free and TOCTOU defects in remap configuration handling. The 8.x branch is affected up to 8.1.9, and administrators still on the 8.x line should migrate to a fixed 9.2.x or 10.1.x release. Refer to the Apache Mailing List Thread for the official announcement and release notes.

Workarounds

No vendor-supplied workaround is documented; upgrading to a fixed version is the recommended remediation.
Reduce the attack surface by minimizing exposure of ATS to untrusted networks until patching is complete.
Avoid frequent live remap configuration reloads on affected versions to reduce the likelihood of triggering the race condition.

bash

# Verify installed Apache Traffic Server version
traffic_server --version

# After upgrading, confirm the running version matches 9.2.15 or 10.1.4
traffic_ctl server status