Description
HTTP::Body versions before 1.23_01 for Perl drop mixed-case percent escapes from urlencoded form fields instead of decoding them. The decode table holds only the all-lowercase and all-uppercase spelling of each hex pair, while the escape pattern matches either case. An escape such as %aB finds no entry and is replaced with nothing, joining the bytes on either side. Hex digits in percent escapes are case-insensitive, and conforming decoders return the byte. A remote attacker can send a field name or value that a conforming decoder in front of the application reads differently, so that pass%aBword reaches the application as password.
References3
Metrics
- CVSS 3.1
-
9.8
CRITICAL
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H - EPSS — exploit probability
- 1% percentile: 49 · as of 7 November 2026
- CWE
- CWE-178
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.