CVE-2026-55199
Description
A vulnerability in libssh2 allows a malicious SSH server to freeze connected clients during the handshake process. By sending a malformed packet, the server triggers a loop that exhausts the client's CPU, resulting in a denial of service.
Statement
A Moderate-rated denial of service vulnerability in the libssh2 client allows a malicious SSH server to freeze the connecting application. By triggering an infinite CPU loop during the initial connection handshake, the server can render the client unresponsive. Note: Red Hat Enterprise Linux (RHEL) 8 and newer are not affected by this flaw, as they do not ship the libssh2 package.
Mitigation
To mitigate this issue, ensure your libssh2 clients only connect to trusted SSH servers. You can enforce this by implementing outbound network access controls (egress filtering) to block applications from initiating connections to unknown or untrusted external hosts.
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 | 7.5 | 5.9 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | High | Low | High |
| Privileges Required | None | None | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | None | None | None |
| Integrity Impact | None | None | None |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:N/AC:L/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)
Availability
Technical Impact: DoS: Resource Consumption (CPU)
Frequently Asked Questions
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