{"id":"CVE-2026-116578","aliases":["GHSA-pw9p-v7r6-gx4p"],"url":"https://o3.security/vulnerability/CVE-2026-116578","summary":"Tornado: Open redirect in RedirectHandler via protocol-relative URLs","details":"### Summary\n\n`tornado.web.RedirectHandler` builds its target URL by substituting parts of the request path into a template. Depending on where those substitutions appear in the template, an attacker can craft a request that redirects to a host of their choosing. This creates an open redirect on the application's domain, which can be used in phishing.\n\n### Impact\n\nApplications are affected if they use `RedirectHandler` with a URL template where a regex capture group can influence the scheme or host of the redirect. This includes:\n\n- **A substitution at the start of the path**, for example `(r\"/(.*)/target\", RedirectHandler, {\"url\": \"/{0}/destination\"})`. A request to `https://example.com//evil.com/target` redirects to `//evil.com/destination`, a protocol-relative URL pointing to evil.com. Variants using backslashes or encoded characters have the same effect, because browsers treat them as equivalent to `//`.\n- **A substitution directly after the host**, for example `(r\"/old(.*)\", RedirectHandler, {\"url\": \"https://new.example.com{0}\"})`. A request to `/old.evil.com/` or `/old@evil.com/` redirects to evil.com.\n- **A template that begins with a substitution** (such as `\"{0}\"`), which can be given an absolute URL.\n\nApplications are not affected if their `RedirectHandler` templates use only static URLs, or if every substitution comes after a fixed host and a `/` (for example `\"/static/{0}\"` or `\"https://example.com/{0}\"`). Other uses of `RequestHandler.redirect()` are not affected by this advisory, although applications that pass user-controlled input to `redirect()` should validate it themselves.\n\n### Patches\n\nFixed in Tornado 6.6. `RedirectHandler` now returns a 400 error if the substituted values would change the scheme or host of the redirect from what the template specifies. As a result, substitutions can no longer be used in the scheme or host part of a template. The similar check in `StaticFileHandler` has also been hardened against backslash and whitespace variants.\n\n### Workarounds\n\n- Change `RedirectHandler` templates so every substitution comes after a fixed prefix ending in `/`, or write capture-group regexes that cannot match characters such as `/`, `\\`, `@`, `.` or `:` where they could affect the host.\n- Alternatively, replace `RedirectHandler` with a custom handler that validates the target before calling `self.redirect()`.\n\n### Credit\n\nReported by Longwei Wang (@gn00295120).","published":"2026-10-26T20:22:32.217Z","modified":"2026-10-28T02:59:29.640922620Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"PyPI","name":"tornado","fixedVersion":"6.6"}],"fix":{"url":"https://github.com/tornadoweb/tornado/commit/940ea725bdd9bc68231d68a105eef17ea6e11233","label":"tornadoweb/tornado@940ea72"},"references":[{"type":"WEB","url":"https://github.com/tornadoweb/tornado/releases/tag/v6.6.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/116xxx/CVE-2026-116578.json"},{"type":"ADVISORY","url":"https://github.com/tornadoweb/tornado/security/advisories/GHSA-pw9p-v7r6-gx4p"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-116578"},{"type":"FIX","url":"https://github.com/tornadoweb/tornado/commit/940ea725bdd9bc68231d68a105eef17ea6e11233"},{"type":"FIX","url":"https://github.com/tornadoweb/tornado/commit/cc75ab0eb3af459c714895a49f682ad354f50117"},{"type":"FIX","url":"https://github.com/tornadoweb/tornado/commit/ccb6a2e5482f17997efd4a74b8200d5b4babc035"},{"type":"FIX","url":"https://github.com/tornadoweb/tornado/pull/3786"},{"type":"PACKAGE","url":"https://github.com/tornadoweb/tornado"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:59:29.640922620Z"}}