CVE-2026-75922
Received Received - Intake

HTTP Request Smuggling in Reverse::Proxy

Publication date: 2026-08-23

Last updated on: 2026-08-23

Assigner: CPANSec

Description
Reverse::Proxy versions before 0.04 for Perl allow HTTP request smuggling via a percent-decoded PATH_INFO written unencoded to the upstream request line. PSGI hands PATH_INFO to an application percent-decoded, so a %XX sequence in the client URL has become a raw byte by the time the proxy sees it. The proxy appends that byte string to the upstream base URL, and for an Upgrade tunnel writes it into a request line it serializes itself, re-encoding nothing in either path. The HTTP client that sends the resulting URL does not validate the target either. A path containing %0d%0a therefore arrives at the upstream as a CRLF that ends the request line, and a decoded space, '?' or '#' truncates it the same way. Everything the client writes after the CRLF is read by the upstream as a second request. On the buffered path it arrives on a keep-alive connection the proxy pools and reuses for other clients. Its method, path and headers are all chosen by the client, and the upstream attributes it to the proxy, so it reaches upstream paths that the proxy's own routing does not expose.

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Meta Information

Published
2026-08-23
Last Modified
2026-08-23
Generated
2026-08-23
AI Q&A
2026-08-23
EPSS Evaluated
N/A
NVD
CVE-2026-75922
EUVD
EUVD-2026-64662

Affected Vendors & Products

Currently, no data is known.

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-444 The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.
CWE-93 The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.

Attack-Flow Graph

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Executive Summary

This vulnerability affects Reverse::Proxy versions before 0.04 for Perl. It allows HTTP request smuggling due to improper handling of percent-decoded PATH_INFO. A client can send a URL with percent-encoded sequences like %0d%0a, which get decoded and appended to the upstream request. This can inject CRLF characters into the request line, splitting it and creating a second malicious request that the upstream server processes as legitimate.

Detection Guidance

Detecting this vulnerability requires checking for HTTP request smuggling attempts, particularly those involving percent-encoded characters like %0d%0a in PATH_INFO. Inspect proxy and server logs for unusual request patterns, such as CRLF sequences or multiple requests arriving on a single connection. Use tools like tcpdump or Wireshark to capture and analyze raw HTTP traffic for malformed request lines.

Impact Analysis

An attacker could exploit this to bypass security controls, access unauthorized resources, or perform actions on behalf of other users. The proxy might route the second request to internal paths not exposed by its normal routing, potentially leading to data breaches or service disruption. The impact depends on the proxy's configuration and the upstream server's behavior.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating GDPR's data protection requirements or HIPAA's security rules for protected health information. Organizations using affected proxies may fail compliance audits if exploited, resulting in legal penalties or reputational damage.

Mitigation Strategies

Immediately update Reverse::Proxy to version 0.04 or later. Configure your proxy to validate and sanitize PATH_INFO before forwarding requests upstream. Disable HTTP/1.1 keep-alive if not required, or implement strict connection pooling policies. Monitor network traffic for signs of exploitation and block suspicious patterns at the firewall level.

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