CVE-2026-89787
Description
A flaw was found in the Linux kernel's ext4 filesystem. A local attacker could craft a directory entry that, when processed during a directory search, leads to an out-of-bounds read. This vulnerability can result in a use-after-free condition, potentially causing a denial of service or information disclosure.
Statement
An out-of-bounds read in ext4 directory lookup can occur for casefolded encrypted directories because ext4_match may read the hash trailer even when only the file name was proven to fit inside the directory block. A crafted directory entry whose name ends at the block boundary can pass the old pre-check while the rounded hash trailer address points past the block end. KASAN reports this as a use-after-free read when the adjacent memory belongs to a freed object. For the CVSS the PR:L is used for the paranoid score because a local user may be able to trigger lookup operations on an already mounted crafted or corrupted ext4 filesystem, while creating or mounting such content usually requires higher privileges. The issue is not network reachable. Impact is at least a local denial of service via kernel crash and in worst case may allow limited confidentiality or integrity impact due to an out-of-bounds kernel read, so it should be reviewed manually.
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 | 5.5 | N/A | N/A |
| Attack Vector | Local | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | Low | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | None | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory
The use of previously freed memory may corrupt valid data, if the memory area in question has been allocated and used properly elsewhere.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If chunk consolidation occurs after the use of previously freed data, the process may crash when invalid data is used as chunk information.
Confidentiality
Technical Impact: Read Memory
Read operations on freed memory can sometimes leak sensitive information instead of causing a crash
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If malicious data is entered before chunk consolidation can take place, it may be possible to take advantage of a write-what-where primitive to execute arbitrary code. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.
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