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How CVE-2026-53043 Works
The vulnerability resides in the Linux kernel’s `ocfs2/dlm` (Oracle Cluster File System 2 Distributed Lock Manager) component. The `dlm_match_regions()` function processes `DLM_QUERY_REGION` network messages. These messages contain a `qr_numregions` field that specifies the number of region entries in the message.
The critical flaw is that `dlm_match_regions()` uses this `qr_numregions` value directly as a loop bound without any validation against the maximum allowed value (O2NM_MAX_REGIONS, which is 32). The `qr_regions` buffer is statically sized to hold at most 32 entries. The `o2net` layer only validates the overall message byte length, not individual field values, so a crafted message can set `qr_numregions` up to 255.
When `qr_numregions` exceeds 32, the loop in `dlm_match_regions()` iterates past the end of the 1024-byte `qr_regions` buffer, causing out-of-bounds (OOB) reads. This can leak kernel memory contents to a remote attacker or trigger a kernel crash, leading to denial of service.
A second bug (fixed in Patch 2) exacerbates the issue: the local-vs-remote comparison loop uses `<=` instead of <, reading one entry past the valid range even when `qr_numregions` is within bounds.
The vulnerability was introduced in kernel version 2.6.37 with commit `ea2034416b54700e30371f2ad6517cbb94674083` and is fixed in various stable releases. The CVSS v3.1 base score is 9.1 (Critical) with vector AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H.
DailyCVE Form:
Platform: ……. Linux Kernel
Version: …….. 2.6.37+
Vulnerability :…… OOB Read
Severity: ……. Critical (9.1)
date: ………. 2026-06-24
Prediction: …… 2026-07-15
What Undercode Say:
Check if your kernel is vulnerable (introduced in 2.6.37)
git log --oneline --grep="ea2034416b54700e30371f2ad6517cbb94674083"
Verify fixed versions (5.10.258+, 5.15.209+, 6.1.175+, 6.6.141+, 6.12.91+, 6.18.33+)
uname -r
Check if OCFS2 module is loaded
lsmod | grep ocfs2
Monitor for DLM_QUERY_REGION messages (requires bpftrace)
bpftrace -e 'kprobe:dlm_match_regions { printf("qr_numregions: %d\n", arg1); }'
Example of a malicious packet construction (conceptual - do not use)
qr_numregions = 255 (exceeds O2NM_MAX_REGIONS=32)
Exploit:
A remote attacker with network access to the DLM service can send a specially crafted `DLM_QUERY_REGION` packet with `qr_numregions` set to a value greater than 32 (up to 255). This causes the kernel to perform out-of-bounds reads past the `qr_regions` buffer. The attack requires no authentication or user interaction. The out-of-bounds reads can leak sensitive kernel memory (e.g., cryptographic keys, process credentials) or cause a system crash (DoS). The off-by-one error (<= instead of <) provides an additional exploitation vector even when `qr_numregions` is within bounds.
Protection:
- Apply Kernel Updates: Upgrade to a fixed version: 5.10.258+, 5.15.209+, 6.1.175+, 6.6.141+, 6.12.91+, or 6.18.33+.
- Backport Patch: Manually apply the patch series “ocfs2/dlm: fix two bugs in dlm_match_regions()” which adds a bounds check for `qr_numregions` before entering loops.
- Network Filtering: Restrict untrusted traffic from reaching the DLM service (port 7777 by default) to reduce exposure to crafted packets.
- Disable OCFS2: If not required, unload the `ocfs2` module (
modprobe -r ocfs2) to eliminate the attack surface.
Impact:
Successful exploitation allows a remote, unauthenticated attacker to:
- Read out-of-bounds kernel memory, potentially disclosing sensitive information such as encryption keys, passwords, or kernel pointers.
- Cause a kernel panic or crash, resulting in a denial of service (DoS).
- The vulnerability affects all Linux distributions that ship the OCFS2 filesystem with the DLM component, including Ubuntu (all LTS releases from 18.04 to 26.04) and other enterprise distributions. The attack is network-accessible, requires no privileges, and has high impact on confidentiality and availability.
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Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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