CVE-2026-76847

Artifact theft and replacement via unchecked run identifiers

Published Aug 24, 2026 · Updated Aug 24, 2026

Missing authorization in Nektos act 0.2.81 through 0.2.89 allows remote attackers to read, overwrite, or delete workflow artifacts. validateRunIDV4 accepts caller-supplied run identifiers without ownership checks, while signed artifact URLs use a shared four-byte HMAC key over ambiguous concatenated fields. Exploitation requires network access to a running Artifacts V4 backend and exposes or replaces build outputs, including stored deployment credentials.

CVSS severity8.7
High
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Missing authorization in Nektos act 0.2.81 through 0.2.89 allows remote attackers to read, overwrite, or delete workflow artifacts. validateRunIDV4 accepts caller-supplied run identifiers without ownership checks, while signed artifact URLs use a shared four-byte HMAC key over ambiguous concatenated fields. Exploitation requires network access to a running Artifacts V4 backend and exposes or replaces build outputs, including stored deployment credentials.

The record

CVE
CVE-2026-76847
Published
Aug 24, 2026
Updated
Aug 24, 2026
Vendor
Nektos
Product
act
Classifications
CWE-862, CWE-321, T1552.001, T1190, T1565.001
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 24, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0.2.81 <=0.2.89

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Nektos · actversion=0.2.81 <=0.2.89

Published CVSS scores

8.7VulnCheckCVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
8.8VulnCheckCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-862Missing Authorization
CWE-321Use of Hard-coded Cryptographic Key
T1552.001Credentials In Files
T1190Exploit Public-Facing Application
T1565.001Stored Data Manipulation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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