Stored XSS via no-op HTML sanitization
Published Apr 9, 2026 · Updated Apr 9, 2026
Stored XSS in the PraisonAI Flask API before 4.5.128 allows remote attackers to execute JavaScript through agent output. The home route converts agent output with markdown.markdown(), then _sanitize_html returns it unchanged when the undeclared nh3 dependency is absent before embedding it in an f-string response. Exploitation requires attacker-controlled content to reach agent output and a user to view the response, allowing browser-session data theft or actions in that user's context.
Summary
What happened
Stored XSS in the PraisonAI Flask API before 4.5.128 allows remote attackers to execute JavaScript through agent output. The home route converts agent output with markdown.markdown(), then _sanitize_html returns it unchanged when the undeclared nh3 dependency is absent before embedding it in an f-string response. Exploitation requires attacker-controlled content to reach agent output and a user to view the response, allowing browser-session data theft or actions in that user's context.
The record
- CVE
- CVE-2026-40112
- Published
- Apr 9, 2026
- Updated
- Apr 9, 2026
- Vendor
- PraisonAI
- Product
- PraisonAI
- Classifications
- CWE-79, T1203
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 9, 2026CVE publishedPublication date reported by the CVE source.
- Apr 9, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 4.5.128
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Vendor advisory stored-XSS proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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