CVE-2026-34956
Description
A flaw was found in Open vSwitch. When Open vSwitch is configured with a conntrack flow using FTP helpers over the userspace datapath, a remote attacker can send a specially crafted FTP stream with an EPASV command exceeding 255 characters. This heap access error can lead to a crash, resulting in a Denial of Service (DoS) for the affected system.
Statement
This vulnerability in Open vSwitch, leading to a heap access error and potential denial of service, is not exploitable in default Red Hat configurations. Exploitation requires Open vSwitch to be specifically configured with FTP helpers over the userspace datapath, which is not enabled by default.
Mitigation
Optionally, avoid using alg=ftp flows. These are not usually configured.
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 | 5.9 | N/A | 5.9 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| 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:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Integrity,Confidentiality,Availability
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of the product's implicit security policy. This can often be used to subvert any other security service.
Availability
Technical Impact: Modify Memory; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU)
Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the product into an infinite loop.
Acknowledgements
Red Hat would like to thank Seiji Sakurai for reporting this issue.
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