CVE-2026-41920: Apache Traffic Server Auth Bypass Flaw

CVE-2026-41920 Overview

CVE-2026-41920 is an Improper Access Control vulnerability [CWE-284] in Apache Traffic Server, a high-performance caching HTTP proxy. The flaw affects versions 9.0.0 through 9.1.14 and 10.0.0 through 10.1.3. The Apache Software Foundation has released fixed versions 9.1.15 and 10.1.4.

The vulnerability is remotely reachable over the network without authentication or user interaction. Its scope impacts the confidentiality and integrity of subsequent systems handled by the proxy, rather than the proxy itself.

Critical Impact
Unauthenticated remote attackers can bypass access controls in Apache Traffic Server, affecting the confidentiality and integrity of downstream systems served through the proxy.

Affected Products

Apache Traffic Server 9.0.0 through 9.1.14
Apache Traffic Server 10.0.0 through 10.1.3
Deployments using Traffic Server as a forward, reverse, or transparent HTTP proxy

Discovery Timeline

2026-07-29 - CVE-2026-41920 published to NVD
2026-07-30 - Last updated in NVD database

Technical Details for CVE-2026-41920

Vulnerability Analysis

Apache Traffic Server acts as a caching HTTP/HTTPS proxy and is commonly deployed at the edge of large content delivery and enterprise networks. The vulnerability sits in the access control logic that governs how the proxy authorizes and forwards requests. An attacker who crafts requests against an exposed Traffic Server instance can reach resources or perform actions that the configured policy should deny.

Because the proxy sits between clients and backend systems, a bypass at this layer affects the security posture of downstream origins. The advisory categorizes the flaw as CWE-284: Improper Access Control, indicating enforcement gaps rather than a memory safety defect.

The attack requires network reachability to the proxy, no privileges, and no user interaction. Exploitation complexity is low, though the flaw depends on specific attack prerequisites present in the target configuration.

Root Cause

The root cause is improper enforcement of access control decisions inside Traffic Server. The proxy fails to consistently reject requests that violate the deployed authorization policy, allowing attackers to reach protected upstream resources or bypass restrictions expected by operators.

Attack Vector

The attack vector is network-based. An attacker sends crafted HTTP requests to an affected Traffic Server instance and receives responses or effects that should have been blocked. Because Traffic Server frequently fronts internal applications, a successful bypass can expose administrative endpoints, cached content, or backend services intended to be gated by the proxy.

No verified proof-of-concept code is published at this time. Refer to the Apache Mailing List Discussion for authoritative technical detail.

Detection Methods for CVE-2026-41920

Indicators of Compromise

Requests to Traffic Server that return 200 OK for paths or origins normally restricted by remap rules or ACL configuration
Unexpected upstream traffic from the Traffic Server host to internal origins that are not part of the documented routing policy
Anomalous Host, X-Forwarded-For, or absolute-URI request lines aimed at bypassing remap or access rules
Access log entries showing successful proxying to administrative or internal endpoints from untrusted client networks

Detection Strategies

Inventory all Apache Traffic Server instances and confirm the running version against 9.1.14 and 10.1.3 boundaries
Compare proxy access logs against the intended remap.config and ACL policy to identify requests that were served but should have been denied
Deploy signatures on upstream web application firewalls that flag requests reaching restricted origins through the Traffic Server layer
Correlate proxy telemetry with origin logs to detect requests arriving at backends without the expected authorization context

Monitoring Recommendations

Forward Traffic Server access.log and error.log to a centralized logging platform for retention and rule-based alerting
Alert on spikes in 2xx responses for URI patterns previously served with 403 or 404 status codes
Monitor for configuration drift on remap.config, ip_allow.yaml, and records.yaml on all proxy hosts

How to Mitigate CVE-2026-41920

Immediate Actions Required

Upgrade Apache Traffic Server to version 9.1.15 or 10.1.4 on all affected hosts
Restrict management and administrative interfaces to trusted networks until the upgrade is complete
Audit remap.config and ip_allow.yaml for rules that assume the proxy enforces access decisions correctly
Review recent proxy access logs for evidence of requests that reached restricted origins

Patch Information

The Apache Software Foundation fixed the issue in Apache Traffic Server 9.1.15 and 10.1.4. Operators running any 9.0.0 through 9.1.14 build must move to 9.1.15, and any 10.0.0 through 10.1.3 build must move to 10.1.4. Details are tracked in the Apache Mailing List Discussion.

Workarounds

Place an additional access control layer, such as a web application firewall, in front of Traffic Server to enforce authorization on sensitive paths
Restrict network reachability to the proxy from untrusted client ranges while patching is scheduled
Enforce authentication at the origin for any backend that previously relied solely on proxy-side access control

bash

# Verify installed Apache Traffic Server version
traffic_server -V

# Example package upgrade on Debian/Ubuntu builds
sudo apt update
sudo apt install --only-upgrade trafficserver

# Restart the service after upgrade
sudo systemctl restart trafficserver

# Confirm the fixed version is running (expect 9.1.15 or 10.1.4)
traffic_server -V