Cyber Resilience

CVE-2026-27469

Medium

Published: 21 February 2026

Published
21 February 2026
Modified
15 April 2026
KEV Added
Patch
CVSS Score v3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
EPSS Score 0.0011 28.6th percentile
Risk Priority 12 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-27469 is a medium-severity Cross-site Scripting (CWE-79) vulnerability in Python (inferred from references). Its CVSS base score is 6.1 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique JavaScript (T1059.007); ranked at the 28.6th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

EU & UK References

Vulnerability details

Isso is a lightweight commenting server written in Python and JavaScript. In commits before 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144, there 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…

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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 is missing entirely from the user-facing comment edit endpoint (PUT /id/) and the moderation edit endpoint (POST /id//edit/). This issue has been patched in commit 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144. To workaround, nabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation, but it does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors.

CWE(s)

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1059.007 JavaScript Execution
Adversaries may abuse various implementations of JavaScript for execution.
T1189 Drive-by Compromise Initial Access
Adversaries may gain access to a system through a user visiting a website over the normal course of browsing.
Why these techniques?

Stored XSS enables arbitrary JavaScript execution in victim browsers (T1059.007) and facilitates drive-by compromise when users view affected pages (T1189).

Confidence: MEDIUM · MITRE ATT&CK Enterprise v18.1

Affected Assets

Python
inferred from references and description; NVD did not file a CPE for this CVE

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

addresses: CWE-79 CWE-116

Output validation against expected content can reject or sanitize script content in generated web pages, reducing XSS exploitability.

addresses: CWE-79

Penetration testing submits XSS payloads to web applications, detecting cross-site scripting flaws for subsequent remediation.

addresses: CWE-79

Validates web inputs to reject script-related content that could produce XSS.

References