Executive brief
Kagi smallweb is a web search application that processes search queries. A flaw in how it renders query strings allows attackers to inject malicious code that executes in users' browsers, potentially stealing session data or hijacking searches. The vulnerability requires a specially crafted HTTP request and does not affect normal browser-based searches, limiting real-world impact.
Technical details
A cross-site scripting (XSS) vulnerability exists in the query string rendering function of app/sw.py in Kagi smallweb. The vulnerability stems from improper sanitization of the qs (query string) parameter in the index function. An attacker can inject unencoded double-quote characters via a raw HTTP request to achieve reflected XSS; ordinary browsers percent-encode quotes as %22, so exploitation requires direct socket communication (e.g., netcat or curl with raw request mode). The attack is remotely exploitable but requires specific preconditions—Werkzeug's request.query_string must receive raw, unencoded input. A patch has been released (commit 00b68144e583f20a6b67e29cf01bc07f57979ffb) and should be applied immediately.
Affected products
- Kagi smallweb up to commit 0ecb9c48edbf98dc7e934b54fbac43869e64b4cf
Timeline
- 2026-09-13: disclosed
- 2026-09-13: patched: Patch commit 00b68144e583f20a6b67e29cf01bc07f57979ffb