CVE-2026-32240
Description
A flaw was found in the KJ-HTTP component of Cap’n Proto when processing HTTP messages that use Transfer-Encoding: chunked. If a chunk size is parsed as a value equal to or greater than 2^64, the value may be truncated when converted to a 64-bit integer. An attacker could exploit this behavior by sending specially crafted HTTP messages containing excessively large chunk sizes. This may cause incorrect interpretation of HTTP message boundaries and could theoretically enable HTTP request or response smuggling in applications that rely on the affected HTTP implementation.
Statement
This issue is rated Moderate severity by Red Hat Product Security, because exploitation requires specially crafted malformed HTTP requests containing extremely large chunk size values that exceed normal protocol limits. Such requests are not generated by typical HTTP clients and may be rejected by intermediary infrastructure such as reverse proxies or load balancers before reaching the affected parser.
Additionally, meaningful exploitation generally depends on differences in how multiple HTTP components interpret malformed chunked encoding values. Because these conditions require non-standard inputs and specific deployment configurations, the attack complexity is considered High. The potential impact is limited to inconsistencies in HTTP request parsing that could enable limited request smuggling scenarios, without directly causing service crashes or enabling arbitrary code execution.
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)
Availability
Technical Impact: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (Memory); DoS: Instability
This weakness can generally lead to undefined behavior and therefore crashes. When the calculated result is used for resource allocation, this weakness can cause too many (or too few) resources to be allocated, possibly enabling crashes if the product requests more resources than can be provided.
Integrity
Technical Impact: Modify Memory
If the value in question is important to data (as opposed to flow), simple data corruption has occurred. Also, if the overflow/wraparound results in other conditions such as buffer overflows, further memory corruption may occur.
Confidentiality,Availability,Access Control
Technical Impact: Execute Unauthorized Code or Commands; Bypass Protection Mechanism
This weakness can sometimes trigger buffer overflows, which can be used to execute arbitrary code. This is usually outside the scope of the product's implicit security policy.
Availability,Other
Technical Impact: Alter Execution Logic; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU)
If the overflow/wraparound occurs in a loop index variable, this could cause the loop to terminate at the wrong time - too early, too late, or not at all (i.e., infinite loops). With too many iterations, some loops could consume too many resources such as memory, file handles, etc., possibly leading to a crash or other DoS.
Access Control
Technical Impact: Bypass Protection Mechanism
If integer values are used in security-critical decisions, such as calculating quotas or allocation limits, integer overflows can be used to cause an incorrect security decision.
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