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CVE-2026-76847— act 0.2.81 through 0.2.89 Missing Authorization in the Artifacts V4 Backend

Quick assessment

Affected
nektos act
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

当工作流使用 或 时，Actions 会启动一个 HTTP Artifacts V4 后端服务。该后端的服务端远程过程调用（RPC）——包括 、 、 、 和 ——接受由调用方提供的 参数，却从未验证该参数是否属于当前请求者。具体而言， 中的 函数虽然解析了该值，但其用于与请求任务（task）的 run ID 进行比较的验证逻辑被注释掉了，导致未执行实际的身份校验。 后端生成的签名 URL 使用一个硬编码为四个字节 的 HMAC 密钥进行认证。该密钥在所有构建版本中完全相同，且签名计算时对端点（endpoint）、过

CVSS 8.8 · High EPSS 0.23% · P13

Affected Version Matrix 1

VendorProduct Version RangeStatus
nektos act 0.2.81≤ 0.2.89 affected
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I. Basic Information for CVE-2026-76847

Vulnerability Information
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Vulnerability Title
act 0.2.81 through 0.2.89 Missing Authorization in the Artifacts V4 Backend
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
授权机制缺失
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
nektos act 0.2.81 ~ 0.2.89 -

II. Public POCs for CVE-2026-76847

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 7571 chars
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III. Intelligence Information for CVE-2026-76847

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Patches & Fixes for CVE-2026-76847 (1)

Vendor Advisories for CVE-2026-76847 (1)

Other References for CVE-2026-76847 (1)

IV. Related Vulnerabilities

Same product: act
Same vendor: nektos
Same weakness: CWE-862

V. Comments for CVE-2026-76847

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