CVE-2026-63385
Description
A flaw was found in libevent. The evhttp_decode_uri_internal function in http.c decodes percent-encoded %00 bytes into literal NUL characters without rejecting them, allowing an attacker to craft a URI such as /admin/secret%00.jpg where extension-based access checks see .jpg but the server processes /admin/secret, bypassing path-based access controls. Additionally, evhttp_header_is_valid_value accepts obsolete HTTP header line folding (CRLF followed by SP/HT), which RFC 9112 states new implementations should reject, creating a header injection vector in proxy chains where the frontend rejects obs-fold but libevent accepts it. This could lead to access control bypass, header injection, or request smuggling.
Statement
Red Hat Enterprise Linux, OpenShift (RHCOS), RHIVOS, and community products (Fedora, Hummingbird) ship affected versions of libevent.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.7 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | High | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | High | N/A | N/A |
| Integrity Impact | High | N/A | N/A |
| Availability Impact | Low | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L
Red Hat CVSS v3 Score Explanation
Converted from CVEORG V4 9.2 (AT:P→AC:H). GHSA rates High, consistent with 7.7.
Understanding the Weakness (CWE)
Integrity,Non-Repudiation,Access Control
Technical Impact: Unexpected State; Hide Activities; Bypass Protection Mechanism
An attacker could create HTTP messages to exploit a number of weaknesses including 1) the message can trick the web server to associate a URL with another URL's webpage and caching the contents of the webpage (web cache poisoning attack), 2) the message can be structured to bypass the firewall protection mechanisms and gain unauthorized access to a web application, and 3) the message can invoke a script or a page that returns client credentials (similar to a Cross Site Scripting attack).
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