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Fencer Vulns
critical 9.3

CVE-2026-27614 json

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

published 2026-02-25 8 mo ago modified 2026-10-27 13 d ago also GHSA-vp6q-7m36-pq3w , PYSEC-2026-301 , EUVD-2026-8597

cvss
9.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 27%
public exploits
0
none known

Summary

Bugsink is a self-hosted error tracking tool. In versions prior to 2.0.13, 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. 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. Successful exploitation requires that the attacker to be able to submit events to the project (i.e. knows the DSN or can access a client that uses it), the Bugsink ingest endpoint is reachable to the attacker, and an administrator explicitly views the crafted event in the UI. Under those conditions, the attacker can execute JavaScript in the administrator’s browser and act with that user’s privileges within Bugsink. Version 2.0.13 fixes the vulnerability.

Patch / fix

  • pypi bugsink 2.0.13
  • bugsink bugsink 2.0.13

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
total
Assessed
8 mo ago

Exploit prediction

0.34% chance of exploitation in the next 30 days, higher than 27% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/bugsink/bugsink/security/advisories/GHSA-vp6q-7m36-pq3w referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 9.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
NVD 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
OSV 3.1 9.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
GitHub 3.1 9.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

Affected packages

ecosystem package affected fixed in
pypi bugsink
<2.0.13
2.0.13

Affected products

  • bugsink bugsink

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.