CVE-2026-76847

HIGHPre-NVD 8.88.8—
EchelonGraph scoreHIGH confidence

Score 8.8 from GitHub Security Advisory (severity: HIGH) published 2026-08-24. a secondary CVSS source baseline 8.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 4 sources updated this week
8.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 8.8Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
8.8
EG Score
8.8(high)
EG Risk
40(Track)
EG Risk 40/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity88% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
13%
KEV
Not listed

Published

August 24, 2026

Last Modified

August 26, 2026

Advisory Details (4)

Auto-updated Aug 24, 2026
No patch confirmed yet.
generic

act 0.2.81 through 0.2.89 Missing Authorization in the Artifacts V4 Backend | Advisories | VulnCheck

https://www.vulncheck.com/advisories/act-through-missing-authorization-in-the-artifacts-v4-backend
generic

act/cmd/root.go at v0.2.89 · nektos/act · GitHub

https://github.com/nektos/act/blob/v0.2.89/cmd/root.go
generic

act/pkg/artifacts/artifacts_v4.go at v0.2.89 · nektos/act · GitHub

https://github.com/nektos/act/blob/v0.2.89/pkg/artifacts/artifacts_v4.go
generic

GitHub - nektos/act: Run your GitHub Actions locally 🚀 · GitHub

https://github.com/nektos/act

Vendor Advisories for CVE-2026-76847(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 26× in last 7d / 26× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-08-30 02:21 UTCEG score recompute
  2. 2026-08-30 02:21 UTCGHSA enrichment
  3. 2026-08-30 01:22 UTCEPSS rescore
  4. 2026-08-29 13:26 UTCGHSA enrichment
  5. 2026-08-29 00:27 UTCEG score recompute
  6. 2026-08-29 00:27 UTCGHSA enrichment
  7. 2026-08-28 21:42 UTCEPSS rescore
  8. 2026-08-28 08:35 UTCGHSA enrichment
  9. 2026-08-27 19:36 UTCEG score recompute
  10. 2026-08-27 19:36 UTCGHSA enrichment
  11. 2026-08-27 14:25 UTCEPSS rescore
  12. 2026-08-27 06:41 UTCGHSA enrichment
  13. 2026-08-26 17:24 UTCEG score recompute
  14. 2026-08-26 17:24 UTCGHSA enrichment
  15. 2026-08-26 16:23 UTCEG score recompute
  16. 2026-08-26 16:23 UTCGHSA enrichment
  17. 2026-08-26 14:47 UTCEPSS rescore
  18. 2026-08-26 05:10 UTCGHSA enrichment
  19. 2026-08-25 16:13 UTCEG score recompute
  20. 2026-08-25 16:13 UTCGHSA enrichment
  21. 2026-08-25 13:49 UTCEPSS rescore
  22. 2026-08-25 03:18 UTCEG score recompute
  23. 2026-08-25 03:18 UTCGHSA enrichment
  24. 2026-08-24 14:24 UTCEG score recompute
  25. 2026-08-24 13:22 UTCEG score recompute
Show 1 more
  1. 2026-08-24 13:22 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-76847?
CVE-2026-76847 is a high vulnerability published on August 24, 2026. 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…
When was CVE-2026-76847 disclosed?
CVE-2026-76847 was first published in the National Vulnerability Database on August 24, 2026, with the most recent update on August 26, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-76847 actively exploited?
CVE-2026-76847 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 86.8% of all scored CVEs.
What is the CVSS score of CVE-2026-76847?
CVE-2026-76847 has a CVSS v3 base score of 8.8 (NVD).
How do I remediate CVE-2026-76847?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-76847, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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