CVE-2026-25542: Tekton Pipelines Auth Bypass Vulnerability

CVE-2026-25542 Overview

CVE-2026-25542 is an Input Validation Error vulnerability in Tekton Pipelines, a Kubernetes-style resource framework for declaring CI/CD-style pipelines. The vulnerability affects versions 0.43.0 through 1.11.0 and stems from improper regex pattern anchoring in the trusted resources verification system. Attackers can bypass verification policies by crafting source strings that contain trusted patterns as substrings, potentially allowing unauthorized code execution in CI/CD pipelines.

Critical Impact

Attackers can bypass trusted resource verification policies in Tekton Pipelines, potentially injecting malicious pipeline tasks or resources into CI/CD workflows by exploiting unanchored regex pattern matching.

Affected Products

• Tekton Pipelines versions 0.43.0 through 1.11.0
• Kubernetes environments running vulnerable Tekton Pipelines releases
• CI/CD systems utilizing Tekton trusted resources verification

Discovery Timeline

• 2026-04-21 - CVE CVE-2026-25542 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-25542

Vulnerability Analysis

The vulnerability exists in Tekton Pipelines' trusted resources verification mechanism. The verification system uses Go's regexp.MatchString function to compare resource source strings (refSource.URI) against patterns defined in spec.resources[].pattern. The critical flaw is that regexp.MatchString in Go reports a match if the pattern matches anywhere within the input string, not just when the entire string matches the pattern.

This behavior means that unanchored regex patterns—including those provided in Tekton's official documentation examples—can be bypassed by crafting malicious source strings that embed the trusted pattern as a substring. When this bypass occurs, the wrong verification mode or cryptographic keys may be applied to a resource, fundamentally undermining the security model of trusted resource verification.

Root Cause

The root cause is classified as CWE-185 (Incorrect Regular Expression). The implementation fails to enforce proper regex anchoring with ^ (start anchor) and $ (end anchor) characters when matching resource source URIs against trusted patterns. Without these anchors, a pattern like github.com/trusted-org/ would match not only legitimate sources but also attacker-controlled URIs such as malicious.com/github.com/trusted-org/fake-path or github.com/trusted-org.attacker.com/.

Attack Vector

The attack vector is network-based, requiring the attacker to have low-privilege access to submit or modify pipeline resources. An attacker can exploit this vulnerability by:

1. Identifying trusted patterns configured in the target Tekton installation's verification policies
2. Crafting a malicious resource source URI that contains the trusted pattern as a substring
3. Submitting the malicious resource, which passes verification due to the substring match
4. Executing unauthorized pipeline tasks with potentially elevated privileges or accessing sensitive secrets

The vulnerability has high impact on integrity as it allows bypass of security controls designed to ensure only trusted code runs in CI/CD pipelines. For example, if a policy trusts resources from github.com/myorg/trusted-repo, an attacker could craft a URI like attacker.com/path/github.com/myorg/trusted-repo/malicious that would incorrectly pass verification.

Detection Methods for CVE-2026-25542

Indicators of Compromise

• Unusual or malformed refSource.URI values in pipeline task definitions containing nested domain patterns
• Pipeline executions sourced from unexpected repositories that appear to match trusted patterns
• Verification policy matches for resources from domains containing legitimate trusted domain names as substrings
• Audit logs showing resource verification passes for sources with suspicious URL structures

Detection Strategies

• Review Tekton verification policy patterns for proper regex anchoring with ^ and $ characters
• Implement logging and alerting for pipeline resource sources that contain URL-like strings within path components
• Audit historical pipeline executions for resources that may have bypassed intended verification policies
• Deploy admission controllers to validate resource source URIs match expected formats before processing

Monitoring Recommendations

• Monitor Tekton controller logs for verification policy matches and analyze the matched source URIs
• Set up alerts for pipeline executions from newly registered or untrusted source repositories
• Implement network egress monitoring to detect connections to unexpected external repositories during pipeline execution
• Review Tekton audit events for anomalous resource verification patterns

How to Mitigate CVE-2026-25542

Immediate Actions Required

• Upgrade Tekton Pipelines to a patched version beyond 1.11.0
• Review all existing verification policy patterns and add proper ^ and $ anchors to regex patterns
• Audit recently executed pipelines for potential exploitation attempts
• Implement additional admission control policies to validate resource sources

Patch Information

The Tekton project has addressed this vulnerability in a commit that fixes the regex pattern matching behavior. Organizations should update to the latest patched release and review the GitHub Security Advisory for complete remediation guidance.

Workarounds

• Manually anchor all verification policy regex patterns with ^ at the start and $ at the end
• Implement strict allowlist-based validation of resource sources at the admission controller level
• Temporarily disable trusted resources verification and rely on alternative security controls until patching is complete
• Use exact string matching instead of regex patterns where possible by escaping all special characters

# Example: Update verification policy patterns with proper anchoring
# Before (vulnerable):
#   pattern: "github.com/myorg/trusted-repo"
#
# After (mitigated):
#   pattern: "^github\\.com/myorg/trusted-repo(/.*)?$"
#
# Verify your Tekton Pipelines version:
kubectl get deployment tekton-pipelines-controller -n tekton-pipelines -o jsonpath='{.spec.template.spec.containers[0].image}'