Isso affected by Stored XSS via comment website field

Exploitation

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

CVSS

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

EPSS

• CVE-2026-27469: 0.26% estimated exploitation activity in the next 30 days; percentile 17.66 (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.

Impact This is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick). The same escaping was missing entirely from the user-facing comment edit endpoint (PUT /id/<id) and the moderation edit endpoint (POST /id/<id/edit/<key). Any visitor to a page embedding isso comments is impacted. No authentication or interaction beyond mouse movement is required to trigger a payload — an attacker can post a comment anonymously (moderation is off by default) with a crafted website URL, and the payload persists in the database and fires on every page load. With the full-page invisible overlay technique…

Published by the source

24 Feb 2026, 16:03 UTC

Last modified by the source

13 Jul 2026, 16:42 UTC

Source last checked

26 Oct 2026, 13:36 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-9fww-8cpr-q66r

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-9fww-8cpr-q66r

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# Patch Next advisory brief: CVE-2026-27469

Advisory: Isso affected by Stored XSS via comment website field
IDs: CVE-2026-27469, GHSA-9fww-8cpr-q66r
Record: https://patchnext.com/advisories/cve-2026-27469 (revision 2, source checked 26 Oct 2026, 13:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: isso 0.13.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI isso: affected < 0.13.2; fixed in 0.13.2

## Suggested inspection (read-only)
- `python -m pip show isso`: 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 isso.
- 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-9fww-8cpr-q66r (OSV record GHSA-9fww-8cpr-q66r lists affected ranges: PyPI isso >=0 <0.13.2 (fixed))
- Verified: https://github.com/advisories/GHSA-9fww-8cpr-q66r (GitHub-reviewed advisory GHSA-9fww-8cpr-q66r lists affected ranges: PyPI isso >=0 <0.13.2)

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