CVE-2026-89695
Description
A flaw was found in the Linux kernel's Network File System Daemon (nfsd). The nfsd4_decode_posixacl() function, responsible for decoding POSIX Access Control Lists (ACLs), does not properly cap the entry count received from a client. A remote attacker can exploit this by sending a specially crafted ACL with an excessively large entry count, leading to unbounded CPU usage during an O(n^2) sorting operation. This can result in a Denial of Service (DoS) for the affected server.
Statement
nfsd4_decode_posixacl accepted a client chosen POSIX ACL entry count from the wire without enforcing NFS_ACL_MAX_ENTRIES. The count is used for allocation and then passed to sort_pacl_range which performs O(n2) sorting, so a crafted NFSv4 compound request can force excessive CPU work in the server processing path. For the CVSS the PR:N is used for the paranoid score because an exposed nfsd endpoint may process the malformed request from a network client before any meaningful authorization decision limits the decode cost. The base score uses PR:L because many real deployments require access to an exported filesystem or valid NFS client credentials. The issue is network reachable when NFSv4 POSIX ACL support is enabled and reachable by the attacker. Impact is denial of service through CPU exhaustion or request processing stalls. No concrete memory corruption primitive is indicated by the patch context.
Mitigation
Mitigation for this issue is either not available or the currently available options don't meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
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 | 9.1 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | High | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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