Docker
CVE-2026-34042
HIGH
GHSA-x34h-54cw-9825
Severity by source
AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N
Primary rating from GitHub Advisory.
CVSS VectorGitHub Advisory
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N
Lifecycle Timeline
4DescriptionGitHub Advisory
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.
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.
AnalysisAI
Unauthenticated remote cache poisoning in nektos/act (GitHub Actions local runner) enables arbitrary code execution by exposing the built-in actions/cache server on all network interfaces without authentication. Attackers who can reach the cache server-including from the public internet if exposed-can inject malicious cache entries with predictable keys, leading to remote code execution within Docker containers running GitHub Actions workflows. No public exploit identified at time of analysis, though EPSS data unavailable. Vendor-released patch available in act v0.2.86.
Technical ContextAI
The nektos/act tool is a Go-based local runner for GitHub Actions workflows that includes a built-in cache server mimicking GitHub's actions/cache functionality. The vulnerability stems from CWE-862 (Missing Authorization), where the cache server binds to 0.0.0.0 (all network interfaces) without implementing authentication or access controls. The ACTIONS_CACHE_URL endpoint accepts cache creation and retrieval requests from any source that can establish a TCP connection. Because GitHub Actions workflows often use predictable cache keys based on dependency files or branch names, an attacker with network access can preemptively populate malicious caches. When a legitimate workflow retrieves what it believes to be a trusted cache, it executes attacker-controlled binaries or scripts within the Docker container context. The affected product is distributed as pkg:go/github.com_nektos_act, commonly used in CI/CD development and testing environments where developers run GitHub Actions locally.
RemediationAI
Upgrade to nektos/act version 0.2.86 or later, which implements authentication for the cache server by appending a secret token to ACTIONS_CACHE_URL to prevent unauthorized access while maintaining compatibility with GitHub's cache action. The fix is available via the GitHub advisory at https://github.com/nektos/act/security/advisories/GHSA-x34h-54cw-9825 and the patched commit at https://github.com/nektos/act/commit/c28c27e141e8b54f9853de82f421ee09846751f7. As an immediate workaround for organizations unable to upgrade, restrict network access to the act cache server port using firewall rules to ensure it only accepts connections from localhost (127.0.0.1), or run act within isolated network segments without internet exposure. Review Docker network configurations to confirm the cache server is not inadvertently exposed on public interfaces. Organizations running Forgejo runners should monitor https://code.forgejo.org/forgejo/runner/issues/294 for additional context on multi-tenant cache isolation improvements being considered upstream.
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View allVendor StatusVendor
SUSE
Severity: High| Product | Status |
|---|---|
| openSUSE Leap 15.6 | Fixed |
| SUSE Linux Enterprise Module for Package Hub 15 SP5 | Fixed |
| SUSE Linux Enterprise Module for Package Hub 15 SP6 | Fixed |
| openSUSE Leap 15.5 | Fixed |
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External POC / Exploit Code
Leaving vuln.today