CVE-2026-32239
Description
A flaw was found in the KJ-HTTP component of Cap’n Proto. When processing HTTP messages, a negative Content-Length value could be implicitly converted to an unsigned integer, resulting in an extremely large length value. An attacker could exploit this behavior by sending specially crafted HTTP messages containing negative Content-Length values. This may lead to inconsistent interpretation of HTTP message boundaries and could theoretically enable HTTP request or response smuggling scenarios in applications that rely on Cap’n Proto’s HTTP implementation.
Statement
This issue is rated Moderate severity by Red Hat Product Security, because exploitation requires the attacker to craft malformed HTTP messages containing negative Content-Length values that trigger the integer conversion behavior in the KJ-HTTP parser. Such malformed inputs are not typically generated during normal HTTP communication and may be rejected or normalized by intermediate HTTP components such as proxies or load balancers or front-end servers before reaching the affected parser. The potential impact is also limited to inconsistent interpretation of HTTP request boundaries, which could enable limited request smuggling scenarios depending on application architecture. The vulnerability does not directly allow remote code execution or service crashes.
Mitigation
Red Hat is not aware of a practical temporary workaround that fully mitigates this issue or meets Red Hat Product Security's standards for usability, deployment, applicability, 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).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 4.8 | 6.5 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | Low | Low | N/A |
| Integrity Impact | Low | Low | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Understanding the Weakness (CWE)
Other,Integrity
Technical Impact: Unexpected State; Quality Degradation
The program could wind up using the wrong number and generate incorrect results. If the number is used to allocate resources or make a security decision, then this could introduce a vulnerability.
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