CVE-2026-34042: act Actions/cache Server Allows Malicious Cache Vulnerability

HIGH
Advisory Identifier: GHSA-x34h-54cw-9825
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CVSS 8.2
CWE-862
Published
Advisory Summary

CVE-2026-34042 is a HIGH (CVSS 8.2) actions/cache server allows malicious cache vulnerability (CWE-862: Missing Authorization) affecting act libraries in the Go ecosystem. The issue involves actions/cache server allows malicious cache injection. Remediation is available by upgrading affected packages to version 0.2.86.

CVE-2026-34042 at a Glance

CVE Identifier CVE-2026-34042
GHSA Identifier GHSA-x34h-54cw-9825
Severity HIGH
CVSS v3.1 Base Score 8.2
CWE Classification CWE-862: Missing Authorization
Affected Product act
Package Ecosystem Go
Published Date
Last Updated

Security Impact

CVSS: 8.2

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction Required (UI:R)
Scope Changed (S:C)
Confidentiality High (C:H)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-34042

To remediate this vulnerability, upgrade all affected act dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

github.com/nektos/act fixed: 0.2.86 
Upgrade github.com/nektos/act to 0.2.86
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for github.com/nektos/act

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-34042, inspect your project dependencies for act:

inspect dependencies for github.com/nektos/act

Analyze the terminal output to locate any version of act in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.2.86), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-862: Missing Authorization, where the product does not perform an authorization check when an actor attempts to access a resource or perform an action. In act, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

act's built-in actions/cache server listens to connections on all interfaces and allows anyone who can connect to it — including someone anywhere on the internet — to create caches with arbitrary keys and retrieve all existing caches. If one can predict which cache keys will be used by local actions, one can create malicious caches containing whatever files one pleases, most likely allowing arbitrary remote code execution within the Docker container. ## Discovery Discovered while discussing [forgejo/runner#294](https://code.forgejo.org/forgejo/runner/issues/294). ## Proposed Mitigation It was discussed to append a secret to `ACTIONS_CACHE_URL` to retain compatibility with GitHub's cache action and still allow authorization. Forgejo is considering also encoding which repo is currently being run in CI into the secret in the URL to prevent unrelated repos using the same (probably global) runner from seeing each other's caches.

CVE-2026-34042 Affected act Versions

1 component(s)
Fixed Versions:
0.2.86
Product / Package Ecosystem Affected Versions Fixed Version
github.com/nektos/act
golang/github.com/nektos/act
Go
< 0.2.86
0.2.86

References

GitHub Advisory / Wiki ADVISORY
https://github.com/nektos/act/security/advisories/GHSA-x34h-54cw-9825
NVD — CVE-2026-34042 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-34042
Security Fix Commit FIX COMMIT
https://github.com/nektos/act/commit/c28c27e141e8b54f9853de82f421ee09846751f7
code.forgejo.org/forgejo/runner/issu... WEB
https://code.forgejo.org/forgejo/runner/issues/294
act Source Repository REPOSITORY
https://github.com/nektos/act
act Release RELEASE
https://github.com/nektos/act/releases/tag/v0.2.86

Frequently Asked Questions

What is CVE-2026-34042?
CVE-2026-34042 is a security vulnerability in act involving actions/cache server allows malicious cache injection under CWE-862: Missing Authorization.
Which act versions are affected?
Affected versions include releases prior to 0.2.86 across affected packages: github.com/nektos/act.
What version fixes CVE-2026-34042?
Upgrading to 0.2.86 (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/nektos/act affected?
Yes, github.com/nektos/act is affected in releases prior to 0.2.86. Upgrade your dependency to 0.2.86 or later.
What is the CVSS score of CVE-2026-34042?
CVE-2026-34042 has a CVSS v3.1 base score of 8.2 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N.
What CWE is associated with CVE-2026-34042?
CVE-2026-34042 is classified under CWE-862: Missing Authorization (The product does not perform an authorization check when an actor attempts to access a resource or perform an action.).
How can I check Go dependencies for CVE-2026-34042?
Run the dependency tree command: 'inspect dependencies for github.com/nektos/act'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-x34h-54cw-9825",
  "modified" : "2026-03-31T18:41:01Z",
  "published" : "2026-03-27T19:35:16Z",
  "aliases" : [ "CVE-2026-34042" ],
  "summary" : "act: actions/cache server allows malicious cache injection",
  "details" : "act's built-in actions/cache server listens to connections on all interfaces and allows anyone who can connect to it — including someone anywhere on the internet — to create caches with arbitrary keys and retrieve all existing caches. If one can predict which cache keys will be used by local actions, one can create malicious caches containing whatever files one pleases, most likely allowing arbitrary remote code execution within the Docker container.\n\n## Discovery\n\nDiscovered while discussing [forgejo/runner#294](https://code.forgejo.org/forgejo/runner/issues/294).\n\n## Proposed Mitigation\n\nIt was discussed to append a secret to `ACTIONS_CACHE_URL` to retain compatibility with GitHub's cache action and still allow authorization. Forgejo is considering also encoding which repo is currently being run in CI into the secret in the URL to prevent unrelated repos using the same (probably global) runner from seeing each other's caches.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/nektos/act"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.2.86"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.2.85"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/nektos/act/security/advisories/GHSA-x34h-54cw-9825"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-34042"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nektos/act/commit/c28c27e141e8b54f9853de82f421ee09846751f7"
  }, {
    "type" : "WEB",
    "url" : "https://code.forgejo.org/forgejo/runner/issues/294"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nektos/act"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nektos/act/releases/tag/v0.2.86"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-862" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-27T19:35:16Z",
    "nvd_published_at" : "2026-03-31T03:15:58Z"
  }
}