Impact
fast-uri decodes percent-encoded characters in the scheme component with the legacy global unescape() and serializes the result back as raw characters, without re-escaping it or validating it as a scheme. A scheme that decodes to characters outside the RFC 3986 scheme grammar can therefore introduce structure the original input did not contain.
For example, %2f%2fevil.example:/pwn parses with no authority (parse().host is undefined), but resolve() and normalize() return //evil.example:/pwn, which reparses with host evil.example. The %uXXXX form (%u002f%u002fevil.example:/pwn) produces the same result, and a scheme containing %0d%0a reaches the output as a raw CR LF.
Applications that normalize or resolve untrusted URLs before a redirect check, host allowlist, or outbound request decision, especially ones that treat a missing authority as same-origin, can be steered to an attacker-chosen authority, and a normalized URI placed in a response header can carry an injected CR LF.
Patches
Upgrade to fast-uri >= 4.1.3, or >= 3.1.6 in the v3.x release line, or >= 2.4.5 in the v2.x release line.
Workarounds
None. Upgrade to the patched version.
References
YashvantHange Reporter
mcollina Remediation developer
UlisesGascon Remediation reviewer
Impact
fast-uridecodes percent-encoded characters in the scheme component with the legacy globalunescape()and serializes the result back as raw characters, without re-escaping it or validating it as a scheme. A scheme that decodes to characters outside the RFC 3986 scheme grammar can therefore introduce structure the original input did not contain.For example,
%2f%2fevil.example:/pwnparses with no authority (parse().hostisundefined), butresolve()andnormalize()return//evil.example:/pwn, which reparses with hostevil.example. The%uXXXXform (%u002f%u002fevil.example:/pwn) produces the same result, and a scheme containing%0d%0areaches the output as a raw CR LF.Applications that normalize or resolve untrusted URLs before a redirect check, host allowlist, or outbound request decision, especially ones that treat a missing authority as same-origin, can be steered to an attacker-chosen authority, and a normalized URI placed in a response header can carry an injected CR LF.
Patches
Upgrade to
fast-uri>= 4.1.3, or >= 3.1.6 in the v3.x release line, or >= 2.4.5 in the v2.x release line.Workarounds
None. Upgrade to the patched version.
References