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Medium, CVSS 6.5amended

Open WebUI: ReDoS in skill-mention regexes causes whole-instance DoS on default config

CVE-2026-59220GHSA-ffpj-xv5c-p3gw

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (open-webui 0.10.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI open-webui

    Affected
    >= 0.9.2, < 0.10.0
    Fixed in
    0.10.0

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
6.5 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-59220: 0.57% estimated exploitation activity in the next 30 days; percentile 47.38 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary Two regexes in backend/openwebui/utils/middleware.py that parse <$skillId|label skill-mention tags backtrack in O(n²) on input that contains <$ followed by a long run with no closing . Both run synchronously, on the asyncio event loop, on every chat completion with no feature gate. Because the default deployment is a single uvicorn worker, one such input pins a CPU core inside re and freezes the entire instance for all users until the worker is killed. Any authenticated user can trigger it with one chat message; it also fires accidentally on benign retrieved content (a RAG chunk or tool output) containing the pattern. Affected versions = 0.9.2, < 0.10.0. Fixed in v0.10.0 (there is no 0.9.7 release). - SKILLMENTIONRE (the extract pattern) has been O(n²) since v0.9.2; exploitable on 0.9.2–0.9.5 with a large input (hundreds of KB). - v0.9.6 added a second, far more aggressive O(n²) in the strip pattern (introduced by the "keep label as readable text" change), so on 0.9.6 a small…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-ffpj-xv5c-p3gw

  2. Revision 1 · created ·

    Published from osv record GHSA-ffpj-xv5c-p3gw

Agent brief

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# Patch Next advisory brief: CVE-2026-59220

Advisory: Open WebUI: ReDoS in skill-mention regexes causes whole-instance DoS on default config
IDs: CVE-2026-59220, GHSA-ffpj-xv5c-p3gw
Record: https://patchnext.com/advisories/cve-2026-59220 (revision 2, source checked 26 Oct 2026, 13:49 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: open-webui 0.10.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI open-webui: affected >= 0.9.2, < 0.10.0; fixed in 0.10.0

## Suggested inspection (read-only)
- `python -m pip show open-webui`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on open-webui.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-ffpj-xv5c-p3gw (OSV record GHSA-ffpj-xv5c-p3gw lists affected ranges: PyPI open-webui >=0.9.2 <0.10.0 (fixed))
- Verified: https://github.com/advisories/GHSA-ffpj-xv5c-p3gw (GitHub-reviewed advisory GHSA-ffpj-xv5c-p3gw lists affected ranges: PyPI open-webui >=0.9.2 <0.10.0)

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