CVE-2026-27469: Isso Package Vulnerable to Stored XSS via Comment Website Field
Summary
CVE-2026-27469: Isso affected by Stored XSS via comment website field. Affects isso versions < 0.13.2. Fixed in 0.13.2. How to fix ↓
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Background
Isso is an open-source commenting system designed for websites, allowing users to engage through comments. It provides features such as moderation, customization, and integration with various platforms. However, a vulnerability has been identified that exposes Isso to stored Cross-Site Scripting (XSS) attacks, particularly through the website field in user comments.
Vulnerability Detail
The vulnerability arises from improper HTML escaping of the website field in Isso's comment system. Specifically, the website field allows single and double quotes to remain unescaped, which can lead to XSS attacks. An attacker can post a comment with a crafted website URL that includes malicious scripts. This payload is stored in the database and executed whenever the comment is loaded, potentially affecting any visitor to the page. The vulnerability does not require authentication or any specific interaction beyond mouse movement, making it particularly dangerous.
How To Fix
Latest published version: 0.14.0 as of 22 Oct 2026
pip install --upgrade "isso==0.14.0"Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
0.13.2
This is the first release that contains the fix.
pip install --upgrade "isso==0.13.2"Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, users can enable comment moderation by setting moderation = enabled = true in the isso.cfg configuration file. This prevents unauthenticated users from posting comments, but it does not fully eliminate the risk if a moderator activates a malicious comment.
Conclusion
The Isso package is vulnerable to a stored XSS attack through the comment website field, allowing attackers to inject malicious scripts. Users are advised to upgrade to version 0.13.2 or later to mitigate this risk. Temporary workarounds are available, but they do not fully eliminate the threat.
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FAQ
The vulnerability is a stored Cross-Site Scripting (XSS) issue that allows attackers to inject malicious scripts through the website field in comments.
Any visitor to a page that embeds Isso comments is at risk, as the vulnerability can be exploited without authentication.
You can use the Vulert playground at Vulert Scanner to check if your application is affected by this vulnerability without needing to sign up.
The CVSS score of this vulnerability is 6.1, indicating a moderate level of severity.
If you cannot upgrade immediately, enable comment moderation in your configuration to reduce the risk of exploitation.
