CVE-2026-59999
Description
A flaw was found in sshd, the OpenSSH server daemon. When DisableForwarding=yes is configured to prevent network traffic forwarding, it incorrectly fails to take precedence over PermitTunnel=yes. This allows a remote attacker to bypass intended security restrictions and establish a tunnel, potentially leading to unauthorized network access or circumvention of security policies, even when forwarding is explicitly disabled.
Statement
This Moderate severity flaw in OpenSSH sshd allows PermitTunnel=yes to override DisableForwarding=yes, potentially bypassing intended security controls. In Red Hat environments where DisableForwarding is used to restrict SSH session capabilities, an attacker who compromises a user's session could still establish a tunnel, leading to unauthorized network access or data exfiltration. This bypass occurs even when administrators explicitly attempt to prevent forwarding, though PermitTunnel is not enabled by default.
Mitigation
To mitigate this issue, if `DisableForwarding=yes` is set in `/etc/ssh/sshd_config` to prevent all forwarding, ensure that `PermitTunnel` is explicitly set to `no` in the same configuration file. This will enforce the intended security policy.
After modifying `/etc/ssh/sshd_config`, restart the `sshd` service for the changes to take effect. This may temporarily interrupt active SSH sessions.
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 | 7.5 | 7.5 | 5.9 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | Low | Low | High |
| Privileges Required | None | None | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | None | None | None |
| Integrity Impact | High | High | High |
| Availability Impact | None | None | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
Frequently Asked Questions
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