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CVE-2026-76847: act

Severity

8.7 (HIGH)

Vendor

NEKTOS

Affected versions

0.2.81 through 0.2.89

Patch status

Unknown

Published

2026-08-24T14:17:02.857

Modified

2026-08-24T14:17:02.857

Why it matters

High-severity vulnerability requiring prioritized review.

Recommended admin actions

• Review and patch based on exposure, asset criticality, and business impact.
• Compare installed versions against the affected version range in the advisory.
• Treat internet-facing systems as higher priority.

Technical summary

act starts an HTTP Artifacts V4 backend whenever a workflow uses actions/upload-artifact@v4 or actions/download-artifact@v4. The control-plane RPCs of that backend, including CreateArtifact, GetSignedArtifactURL, ListArtifacts, FinalizeArtifact and DeleteArtifact, accept a caller-supplied workflow_run_backend_id and never check that it belongs to the requester: validateRunIDV4 in pkg/artifacts/artifacts_v4.go parses the value and returns it with the comparison against the requesting task's run ID left commented out. The signed URLs the backend issues are authenticated by an HMAC whose key is hardcoded to the four bytes 0xba 0xdb 0xee 0xf0, identical in every build, computed over a concatenation of endpoint, expiry, artifact name and task ID with no length prefix or delimiter, so signatures are both forgeable and ambiguous between differing artifact name and task ID pairs. The –artifact-server-addr flag defaults to the host's outbound address rather than loopback, leaving the backend reachable from the surrounding network. Any client that can reach it may read, overwrite or delete the artifacts of a concurrently running job with no credentials, exposing build outputs such as secrets and deployment credentials and permitting their replacement before the owning job consumes them.

View the official NVD record for CVE-2026-76847

CVE data is sourced from NVD/CNA records and optional enrichment. Validate against the vendor advisory before taking production action.