GHSA-9fww-8cpr-q66r

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Source
https://github.com/advisories/GHSA-9fww-8cpr-q66r
Import Source
https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/02/GHSA-9fww-8cpr-q66r/GHSA-9fww-8cpr-q66r.json
JSON Data
https://api.osv.dev/v1/vulns/GHSA-9fww-8cpr-q66r
Aliases
Published
2026-02-24T16:03:04Z
Modified
2026-02-24T16:23:27.959194Z
Severity
  • 6.1 (Medium) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N CVSS Calculator
Summary
Isso affected by Stored XSS via comment website field
Details

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 described in the report, the victim only needs to move their mouse.

Patches

The issue is fixed in commit 3cf27c2. Users should upgrade to a version containing that commit once released. The fix applies html.escape(..., quote=True) to the website field across all three write paths (POST /new, PUT /id/<id>, POST /id/<id>/edit/<key>), and adds input validation and escaping to the moderation edit endpoint which previously had neither.

Workarounds

Enabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation. However, it does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors. There is no configuration-only workaround that fully prevents the vulnerability.

Resources

  • https://docs.python.org/3/library/html.html#html.escape — note the quote parameter
Database specific 
{
    "github_reviewed": true,
    "github_reviewed_at": "2026-02-24T16:03:04Z",
    "severity": "MODERATE",
    "nvd_published_at": "2026-02-21T08:16:11Z",
    "cwe_ids": [
        "CWE-116",
        "CWE-79"
    ]
}
References

Affected packages

PyPI / isso

Package

Name
isso
View open source insights on deps.dev
Purl
pkg:pypi/isso

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected
Fixed
0.13.2

Affected versions

0.*
0.8
0.8.1
0.8.2
0.8.3
0.9
0.9.1
0.9.2
0.9.3
0.9.4
0.9.5
0.9.6
0.9.7
0.9.8
0.9.9
0.9.10
0.10
0.10.1
0.10.2
0.10.3
0.10.4
0.10.5
0.10.6
0.11.0
0.11.1
0.12.0
0.12.1
0.12.2
0.12.4
0.12.5
0.12.6
0.12.6.1
0.12.6.2
0.13.0
0.13.1.dev0

Database specific

source 
"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/02/GHSA-9fww-8cpr-q66r/GHSA-9fww-8cpr-q66r.json"