{"schema_version":"1.7.5","id":"GHSA-pr2v-jx2c-wg9f","published":"2026-07-20T18:55:11Z","modified":"2026-07-20T19:00:24.953994999Z","aliases":["CVE-2025-67724","PYSEC-2025-265"],"summary":"Tornado vulnerable to Header Injection and XSS via reason argument","details":"# Header injection and XSS via `reason` argument\n\n## Summary\n\nThe `reason` argument (used by both `RequestHandler.set_status` and `tornado.web.HTTPError` is designed to allow applications to pass custom \"reason\" phrases (the \"Not Found\" in `HTTP/1.1 404 Not Found`) to the HTTP status line (mainly for non-standard status codes). Vulnerabilities exist in Tornado versions prior to 6.5.3 if untrusted data is passed as the `reason` argument.\n\n## Details\n\nIn vulnerable versions, the supplied `reason` phrase is used unescaped in HTTP headers (where it could be used for header injection) or in HTML in the default error page (where it could be used for XSS).\n\n## Impact\n\n* **Type:** Reflected Cross-Site Scripting (CWE-79) in default error page, or header injection (CWE-644)\n* **Actors:** Remote attacker who can cause the application to raise `HTTPError`/`set_status` with an attacker-controlled `reason` (e.g., via query parameter used by developer).\n* **Effect:** Execution of arbitrary JavaScript in victims' browsers when they view the error page — possible session token theft, CSRF escalation, UI spoofing, or other client-side attacks depending on context.\n* **Scope:** Only applications that explicitly reflect untrusted input into `reason` are affected.\n\n## Mitigation\n\nAside from upgrading to Tornado 6.5.3 or newer, the vulnerability can be mitigated by not using untrusted data for the `reason` argument. In the intended use case the `reason` argument would generally be a string literal and not derived from user input. Also, the `reason` argument is rarely required (reason phrases are not used at all in HTTP/2) and can generally be omitted.\n\nFor a general-purpose error message in HTTPError, consider using the `log_message` argument instead of `reason`.","affected":[{"package":{"name":"tornado","ecosystem":"PyPI","purl":"pkg:pypi/tornado"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.5.3"}]}],"versions":["0.2","1.0","1.1","1.1.1","1.2","1.2.1","2.0","2.1","2.1.1","2.2","2.2.1","2.3","2.4","2.4.1","3.0","3.0.1","3.0.2","3.1","3.1.1","3.2","3.2.1","3.2.2","4.0","4.0.1","4.0.2","4.1","4.1b2","4.2","4.2.1","4.2b1","4.3","4.3b1","4.3b2","4.4","4.4.1","4.4.2","4.4.3","4.4b1","4.5","4.5.1","4.5.2","4.5.3","4.5b1","4.5b2","5.0","5.0.1","5.0.2","5.0a1","5.0b1","5.1","5.1.1","5.1b1","6.0","6.0.1","6.0.2","6.0.3","6.0.4","6.0a1","6.0b1","6.1","6.1b1","6.1b2","6.2","6.2b1","6.2b2","6.3","6.3.1","6.3.2","6.3.3","6.3b1","6.4","6.4.1","6.4.2","6.4b1","6.5","6.5.1","6.5.2","6.5b1"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/07/GHSA-pr2v-jx2c-wg9f/GHSA-pr2v-jx2c-wg9f.json"}}],"references":[{"type":"WEB","url":"https://github.com/tornadoweb/tornado/security/advisories/GHSA-pr2v-jx2c-wg9f"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-67724"},{"type":"WEB","url":"https://github.com/tornadoweb/tornado/commit/9c163aebeaad9e6e7d28bac1f33580eb00b0e421"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/tornado/PYSEC-2025-265.yaml"},{"type":"PACKAGE","url":"https://github.com/tornadoweb/tornado"},{"type":"WEB","url":"https://github.com/tornadoweb/tornado/releases/tag/v6.5.3"}],"database_specific":{"cwe_ids":["CWE-79"],"github_reviewed":true,"github_reviewed_at":"2026-07-20T18:55:11Z","nvd_published_at":"2025-12-12T06:15:41Z","severity":"MODERATE"},"severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N"}]}