CVE-2026-90995
Description
A flaw was found in SSSD (System Security Services Daemon). A local attacker with privileges to connect to the PAM (Pluggable Authentication Modules) responder socket can send a specially crafted protocol request. If the pam_app_services configuration is enabled and the service item is omitted from the request, a NULL pointer dereference can occur. This vulnerability leads to a denial of service, causing the PAM responder to crash and disrupt authentication services.
Statement
This Moderate impact denial of service vulnerability in SSSD's PAM responder requires local access and a non-default pam_app_services configuration. An authenticated local attacker can send a crafted PAM request, leading to a NULL pointer dereference and crashing the PAM responder, thereby disrupting authentication services. The default SSSD configuration is not affected.
Mitigation
To mitigate this issue, avoid configuring `pam_app_services` in the `[pam]` section of `/etc/sssd/sssd.conf` if it is not operationally required. If `pam_app_services` is configured, remove or comment out the `pam_app_services` line and restart the `sssd` service.
Example:
# /etc/sssd/sssd.conf
[pam]
# pam_app_services = app_svc
After modifying the configuration, restart the SSSD service:
`systemctl restart sssd`
Note that restarting the SSSD service may temporarily interrupt authentication and authorization services.
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 | 5.5 | N/A | 5.5 |
| Attack Vector | Local | N/A | Local |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | Low | N/A | Low |
| 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:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart
NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation.
Integrity,Confidentiality
Technical Impact: Execute Unauthorized Code or Commands; Read Memory; Modify Memory
In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution.
Acknowledgements
This issue was discovered by Found by AISLE in partnership with Red Hat.
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