Bugsink is vulnerable to Stored XSS via Pygments fallback in stacktrace rendering

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

EPSS

• CVE-2026-27614: 0.34% estimated exploitation activity in the next 30 days; percentile 27.10 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary An unauthenticated attacker who can submit events to a Bugsink project can store arbitrary JavaScript in an event. The payload executes only if a user explicitly views the affected Stacktrace in the web UI.

Details When Pygments returns more lines than it was given (a known upstream quirk that triggers with Ruby heredoc-style input), `_pygmentize_lines()` in `theme/templatetags/issues.py:75-77` falls back to returning the raw input lines. `mark_safe()` at line 111-113 is then applied unconditionally - including to those unsanitized raw lines. Since DSN endpoints are public by Sentry protocol, no account is needed to inject. The payload sits in the database until an admin looks at the event. ```python

issues.py:75-77 - fallback path, no escaping if len(pygmented) != len(lines): return lines

raw HTML returned here

issues.py:111-113 - unconditional mark_safe return [mark_safe(line) for line in result] ```

Operational Signals Exploitation attempts are likely to…

Published by the source

25 Feb 2026, 16:06 UTC

Last modified by the source

27 Oct 2026, 15:30 UTC

Source last checked

28 Oct 2026, 06:10 UTC

1. Revision 5 · amended · 28 Oct 2026

   Amended from osv record GHSA-vp6q-7m36-pq3w

2. Revision 4 · amended · 27 Oct 2026

   Amended from ghsa record GHSA-vp6q-7m36-pq3w

3. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-vp6q-7m36-pq3w

4. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-vp6q-7m36-pq3w

5. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-vp6q-7m36-pq3w

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# Patch Next advisory brief: CVE-2026-27614

Advisory: Bugsink is vulnerable to Stored XSS via Pygments fallback in stacktrace rendering
IDs: CVE-2026-27614, GHSA-vp6q-7m36-pq3w
Record: https://patchnext.com/advisories/cve-2026-27614 (revision 5, source checked 28 Oct 2026, 06:10 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: bugsink 2.0.13. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI bugsink: affected < 2.0.13; fixed in 2.0.13

## Suggested inspection (read-only)
- `python -m pip show bugsink`: 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 bugsink.
- 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://github.com/advisories/GHSA-vp6q-7m36-pq3w (GitHub-reviewed advisory GHSA-vp6q-7m36-pq3w lists affected ranges: PyPI bugsink >=0 <=2.0.12)
- Verified: https://osv.dev/vulnerability/GHSA-vp6q-7m36-pq3w (OSV record GHSA-vp6q-7m36-pq3w lists affected ranges: PyPI bugsink >=0 <2.0.13 (fixed))

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