CVE-2026-16254: ClairCore APK Scanner DoS Vulnerability

CVE-2026-16254 Overview

CVE-2026-16254 is a denial-of-service vulnerability in claircore, the container image analysis library used by the Clair vulnerability scanner. The flaw resides in the Alpine Package Keeper (APK) package scanner. A malformed package database within a container layer triggers an out-of-bounds read [CWE-125] during parsing. The resulting Go panic is not recovered by the caller, which crashes the Clair indexer process. Attackers who can submit container images for scanning can repeatedly disrupt indexing operations, degrading availability of the vulnerability management pipeline.

Critical Impact
Malformed APK package-database data in an untrusted container layer crashes the Clair indexer through an unrecovered panic, producing a denial of service against the scanning service.

Affected Products

Claircore APK package scanner
Clair vulnerability scanner (indexer component)
Red Hat products embedding affected Claircore versions

Discovery Timeline

2026-07-20 - CVE-2026-16254 published to the National Vulnerability Database
2026-07-21 - Last updated in NVD database

Technical Details for CVE-2026-16254

Vulnerability Analysis

Claircore parses package metadata from container layers to correlate installed software against vulnerability data. The APK scanner reads the on-disk installed-database format used by Alpine Linux. When the scanner encounters truncated or malformed structures, it performs slice or index operations without validating the underlying length. The resulting out-of-bounds access raises a Go runtime panic. Because the panic is not caught by a recover in the scanner's goroutine, it propagates upward and terminates the Clair indexer process. Restarting the process does not remediate the issue: resubmitting the same crafted image will crash the service again, producing a persistent denial-of-service condition against the scanning pipeline.

Root Cause

The root cause is missing bounds validation in the APK package-database parsing path combined with the absence of panic recovery at the scanner boundary. The CWE-125 classification reflects the out-of-bounds read against parsed byte buffers or slices derived from attacker-controlled input.

Attack Vector

Exploitation requires network access to a Clair or Claircore-based scanning service and the ability to submit a container image or layer for analysis. An authenticated user with permission to push images to a registry monitored by Clair, or to request a manifest scan, can supply a container layer containing a malformed APK installed-database file. When the indexer pulls and parses the layer, the panic terminates the process. No confidentiality or integrity impact is expected; the effect is limited to service availability.

See the Red Hat CVE Advisory and Red Hat Bug Report #2502701 for upstream technical details.

Detection Methods for CVE-2026-16254

Indicators of Compromise

Repeated crashes or restarts of the Clair indexer process with Go panic stack traces referencing the APK scanner package.
Failed or stalled index operations correlated with specific container image digests submitted by a single tenant or user.
Log entries containing runtime error: index out of range or slice bounds out of range originating in claircore/apk code paths.

Detection Strategies

Aggregate Clair indexer logs in a central logging platform and alert on Go panic signatures tied to the APK scanner.
Correlate image push events in the container registry with subsequent indexer crashes to identify the offending layer and submitter.
Track process restart counts for the Clair indexer container or pod through orchestrator metrics such as Kubernetes restartCount.

Monitoring Recommendations

Alert when indexer restart rates exceed baseline over a rolling window to catch repeated exploitation attempts.
Retain crashed image digests and associated manifests for forensic review and blocklisting.
Monitor scan queue depth and time-to-index latency, since a crashing indexer will produce visible backlog growth.

How to Mitigate CVE-2026-16254

Immediate Actions Required

Upgrade Claircore and Clair to a fixed release once the upstream maintainers publish patched versions referenced in the Red Hat advisory.
Restrict which users and service accounts can submit images for scanning to reduce the attacker population.
Quarantine any container images identified as triggering the panic and remove them from the scan queue.

Patch Information

Patched versions will be distributed through the upstream claircore and clair projects and by downstream vendors. Consult the Red Hat CVE Advisory for product-specific fix availability and errata references. Apply vendor updates as they become available, and rebuild any container images that bundle Claircore as a library.

Workarounds

Run the Clair indexer under a supervisor or orchestrator that restarts the process automatically to reduce downtime while a patch is being applied.
Gate image submission behind authenticated, rate-limited APIs to slow repeat exploitation.
Temporarily disable APK scanning if the deployment does not index Alpine-based images and configuration permits selective scanner activation.

bash

# Configuration example: restart policy for the Clair indexer container
# (Kubernetes Deployment snippet)
spec:
  template:
    spec:
      restartPolicy: Always
      containers:
        - name: clair-indexer
          image: quay.io/projectquay/clair:<patched-tag>
          livenessProbe:
            httpGet:
              path: /healthz
              port: 8080
            periodSeconds: 10
            failureThreshold: 3