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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.

nektos Act是nektos组织开源的一款本地执行持续集成工作流的命令行工具。 nektos Act 0.2.81版本至0.2.89版本存在安全漏洞，该漏洞源于Artifacts V4后端控制平面RPC未验证调用者提供的workflow_run_backend_id，且HMAC签名密钥硬编码可伪造，后端默认监听非回环地址，可能导致网络中的攻击者无凭据读取、覆盖或删除并发任务工件，泄露并替换构建输出中的敏感凭据。

CVSS 8.8 · High EPSS 0.35% · P27

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
Vulnerability Title
nektos Act 加密问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
nektos Act是nektos组织开源的一款本地执行持续集成工作流的命令行工具。 nektos Act 0.2.81版本至0.2.89版本存在安全漏洞，该漏洞源于Artifacts V4后端控制平面RPC未验证调用者提供的workflow_run_backend_id，且HMAC签名密钥硬编码可伪造，后端默认监听非回环地址，可能导致网络中的攻击者无凭据读取、覆盖或删除并发任务工件，泄露并替换构建输出中的敏感凭据。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

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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