CVE-2026-0966
Description
A flaw was found in libssh. The API function ssh_get_hexa() is vulnerable to a denial of service when processing zero-length input. This can be exploited remotely by an attacker during GSSAPI (Generic Security Service Application Program Interface) authentication if the server's logging verbosity is set to SSH_LOG_PACKET (3) or higher. Successful exploitation could lead to a self-Denial of Service of the per-connection daemon process.
Statement
Attack Complexity is high as it requires the logging verbosity to be set to SSH_LOG_PACKET (3) or higher, which is not the default configuration in Red Hat Enterprise Linux.
Mitigation
To mitigate this issue, consider disabling GSSAPI authentication if it is not required, or reduce the `LogLevel` in the `sshd_config` file to a value lower than `SSH_LOG_PACKET` (e.g., `INFO`).
To disable GSSAPI authentication, add or modify the following line in `/etc/ssh/sshd_config`:
`GSSAPIAuthentication no`
To reduce logging verbosity, add or modify the following line in `/etc/ssh/sshd_config`:
`LogLevel INFO`
After making changes to `sshd_config`, the `sshd` service must be restarted 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 | 6.5 | 8.2 | 6.5 |
| 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 | Low | Low | Low |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
cve.org: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
Understanding the Weakness (CWE)
Integrity,Availability
Technical Impact: Modify Memory; DoS: Crash, Exit, or Restart
Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash.
Integrity,Confidentiality,Availability,Access Control,Other
Technical Impact: Execute Unauthorized Code or Commands; Modify Memory; Bypass Protection Mechanism; Other
If the corrupted memory can be effectively controlled, it may be possible to execute arbitrary code. If the corrupted memory is data rather than instructions, the system will continue to function with improper changes, possibly in violation of an implicit or explicit policy. The consequences would only be limited by how the affected data is used, such as an adjacent memory location that is used to specify whether the user has special privileges.
Access Control,Other
Technical Impact: Bypass Protection Mechanism; Other
When the consequence is arbitrary code execution, this can often be used to subvert any other security service.
Acknowledgements
Red Hat would like to thank Jakub Jelen (libssh), Jun Xu, Kang Yang, and Yunhang Zhang for reporting this issue.
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