CVE-2026-76847act 0.2.81 through 0.2.89 Missing Authorization in the Artifacts V4 Backend
- 8.7HighCVSS base score
- 0.35%Exploitation in 30 daysEPSS · top 71% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
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.
Timeline
ID reserved
By VulnCheck
- 5 days later
· 5 days later
Published
- 2 days later
· 2 days later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| VulnCheckCNA (assigner) | 4.0 | High8.7 | CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N |
| VulnCheckCNA (assigner) | 3.1 | High8.8 | CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| NVDNVD · Deferred | 4.0 | High8.7 | CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X |
- EPSS (exploitation in 30 days)
- 0.35% · top 71% of all CVEs (15 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: total
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.7.
Affected products
References
References4
- https://github.com/nektos/act (opens in a new tab)product
- https://github.com/nektos/act/blob/v0.2.89/pkg/artifacts/artifacts_v4.go (opens in a new tab)technical-description
- https://github.com/nektos/act/blob/v0.2.89/cmd/root.go (opens in a new tab)technical-description
- VulnCheck Advisory: act 0.2.81 through 0.2.89 Missing Authorization in the Artifacts V4 Backend (opens in a new tab)third-party-advisory
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-64852 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-76847)Record last updated .