CVE-2026-9675
Description
A flaw was found in undici. A malicious WebSocket server could exploit this vulnerability by sending fragmented messages that individually meet size limits but collectively exceed them. This can lead to unbounded memory growth in the client process, resulting in memory exhaustion and a denial of service (DoS).
Statement
This is rated Moderate by Red Hat (CVSS 5.9) because successful exploitation requires the undici WebSocket client to connect to an attacker-controlled server (AC:H), which is unlikely in typical Red Hat product deployments where WebSocket endpoints are trusted internal services. No Red Hat product is affected — all streams shipping undici bundle versions 5.x through 7.x, which are outside the vulnerable range of 8.0.0 to 8.4.x. The vulnerable code path (unbounded WebSocket frame accumulation) was introduced in undici 8.0.0 and is not present in earlier major versions.
Mitigation
Red Hat products that bundle the undici HTTP client ship versions 5.x, 6.x, and 7.x, which do not contain the vulnerable WebSocket frame accumulation code path introduced in undici 8.0.0. No Red Hat product streams are affected by this vulnerability. Users who have manually installed undici 8.x outside of Red Hat-provided packages should upgrade to undici 8.5.0 or later to fully resolve this issue.
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 | 5.9 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Resource Consumption (Other)
If an attacker can trigger the allocation of the limited resources, but the number or size of the resources is not controlled, then the most common result is denial of service. This would prevent valid users from accessing the product, and it could potentially have an impact on the surrounding environment, i.e., the product may slow down, crash due to unhandled errors, or lock out legitimate users. For example, a memory exhaustion attack against an application could slow down the application as well as its host operating system.
Access Control,Other
Technical Impact: Bypass Protection Mechanism; Other
In some cases it may be possible to force the product to "fail open" in the event of resource exhaustion. The state of the product -- and possibly the security functionality - may then be compromised.
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