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Linux Kernel EUVDEUVD-2026-38883

| CVE-2026-53015 MEDIUM
2026-06-24 Linux GHSA-v64f-8vqx-f88g
Information Disclosure Linux
5.5
CVSS 3.1 · NVD
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Obtain low-privilege shell on 32-bit Linux host
  2. Delivery
    Access mounted EROFS filesystem with large cluster offset
  3. Exploit
    Trigger `lcn << lclusterbits` integer truncation
  4. Execution
    Kernel computes corrupted block address
  5. Impact
    Kernel crash / availability loss

Vulnerability Assessment

Exploitation Conditions

Exploitation requires all three of the following conditions simultaneously: (1) the host kernel must be running on a 32-bit architecture (i386, ARM32, MIPS32, etc.) where unsigned long is 32 bits wide - 64-bit systems are categorically unaffected; (2) an EROFS filesystem must be mounted and accessible to the local attacker; (3) the filesystem image must contain files or metadata whose logical cluster numbers, when shifted by lclusterbits, produce an offset exceeding 4 GiB (2^32 bytes). The CVSS vector (PR:L) confirms that low-privilege local access is sufficient - no administrator or root access is required to trigger the bug once the filesystem is mounted. Active exploitation is limited to: 32-bit-only hardware platforms, EROFS filesystem availability, and file sizes or metadata layouts that cross the 4 GiB cluster boundary.
Impact

The CVSS 3.1 vector (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, score 5.5) accurately reflects the constrained attack surface: exploitation is strictly local, requires only low privileges, and yields no confidentiality or integrity impact - only availability. The real-world risk is further bounded by two architectural constraints that the CVSS score does not capture: the bug only manifests on 32-bit kernels (where unsigned long is 32 bits), and only when EROFS is actively in use with files or metadata located beyond the 4 GiB cluster boundary. 32-bit production Linux deployments are a shrinking population, largely confined to embedded, IoT, and legacy hardware. EPSS at 0.17% (6th percentile) corroborates that automated or opportunistic exploitation is highly unlikely. The vulnerability is not in CISA KEV, and no public exploit code has been identified. This is a genuine but low-urgency correctness fix rather than a high-priority security emergency; priority should be given to 32-bit systems running EROFS in environments such as Android build servers, embedded Linux appliances, or legacy i386/ARM32 deployments.
Exploit ScenarioDerived

A local user on a 32-bit Linux system (e.g., an i386 or ARM32 device) mounts or accesses an EROFS filesystem image that contains data or metadata whose logical cluster number translates to a byte offset exceeding 4 GiB. The truncated LCN causes the kernel to compute an incorrect block address, potentially triggering a kernel BUG, NULL dereference, or similar fatal condition that crashes the system. No public proof-of-concept has been identified; a crafted EROFS image designed to place clusters at the 4 GiB boundary would be the most direct exploit primitive.
This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.2% exploitation probability (EPSS)

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AnalysisAIv1 – Jul 15, 2026

Integer truncation in the Linux kernel's EROFS filesystem driver on 32-bit platforms causes logical cluster number (LCN) calculations to overflow at the 4 GiB boundary, resulting in incorrect block addressing and potential kernel-level availability impact. Affected systems are those running 32-bit Linux kernels (where unsigned long is 32 bits wide) with EROFS filesystems mounted. No public exploit exists and no active exploitation has been confirmed; EPSS stands at a very low 0.17% (6th percentile), consistent with the niche attack surface of 32-bit deployments.

RemediationAI

The primary fix is to upgrade to a patched stable kernel release: 6.12.91, 6.18.33, 7.0.10, or 7.1, all of which contain the u64 unification commits available at https://git.kernel.org/stable/. Distribution maintainers should apply the relevant stable-queue patch to their supported kernels. For environments where an immediate kernel upgrade is not feasible, a targeted workaround is to avoid mounting EROFS images whose content extends beyond the 4 GiB cluster boundary on 32-bit hosts; this eliminates the trigger condition without impacting systems that only use EROFS for small images. Alternatively, replacing EROFS with a different read-only filesystem (e.g., SquashFS) on affected 32-bit hosts eliminates exposure entirely, though this requires application-level changes. No workaround addresses the root arithmetic bug; patching is the only complete fix.

Affected VersionsENISA

Linux patch: 0
Linux patch: 6.12.91
Linux 152a333a589560bee002e4c96761f1b560a5793c <582b0bf201157632cb5474c885989a6ebda46521
Linux patch: 7.0.10
Linux patch: 6.18.33
Linux 152a333a589560bee002e4c96761f1b560a5793c <2d8c7edcb661812249469f4a5b62e9339118846f
Linux patch: 7.1
Linux 152a333a589560bee002e4c96761f1b560a5793c <858e4d98a86adf34584767388deb6c9b217f70c5
Linux 152a333a589560bee002e4c96761f1b560a5793c <4fc9b12e43a3f19a01a8fb61f7961be79de20253
Linux 5.3

Affected Packages

euvd linux no fix

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

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Technical ContextAI · show details

EROFS (Enhanced Read-Only File System) is a compressed, space-efficient read-only filesystem introduced in Linux 5.3, commonly used in Android and embedded systems. The root cause is an integer width mismatch: the lcn (logical cluster number) variable was declared as unsigned long or unsigned int, which is only 32 bits wide on 32-bit architectures (CPE: cpe:2.3:a:linux:linux). When the kernel computes lcn << lclusterbits to derive a byte offset, the result silently wraps at 4 GiB (2^32), producing a corrupted address for any cluster residing beyond that boundary. The fix unifies lcn as the explicit u64 type throughout the EROFS codebase to guarantee 64-bit arithmetic regardless of the host architecture. While no CWE is formally assigned, the root cause class is an implicit type narrowing / integer truncation error analogous to CWE-190 (Integer Overflow) or CWE-681 (Incorrect Conversion Between Numeric Types).

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  • Exploit and PoC references, threat intelligence from 22 sources
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Severity by source

NVD PRIMARY 5.5 MEDIUM
AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
vuln.today AI 5.5 MEDIUM

Local access and low privileges suffice to trigger the truncation via EROFS access; no confidentiality or integrity impact, only availability loss through potential kernel crash.

3.1 AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.0 AV:L/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE MEDIUM
Red Hat 5.5 LOW

Primary rating from NVD.

CVSS VectorNVD

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

4
CVSS changed
Jul 15, 2026 - 14:07 NVD
5.5 (MEDIUM)
Patch available
Jun 24, 2026 - 18:02 EUVD
CVE Published
Jun 24, 2026 - 16:29 nvd
MEDIUM 5.5
CVE Published
Jun 24, 2026 - 16:29 cve.org
UNKNOWN (no severity yet)

DescriptionNVD

In the Linux kernel, the following vulnerability has been resolved:

erofs: unify lcn as u64 for 32-bit platforms

As sashiko reported [1], lcn was typed as unsigned long (or unsigned int sometimes), which is only 32 bits wide on 32-bit platforms, which causes (lcn << lclusterbits) to be truncated at 4 GiB.

In order to consolidate the logic, just use u64 consistently around the codebase.

[1] https://sashiko.dev/r/20260420034612.1899973-1-hsiangkao%40linux.alibaba.com

Threat Intelligence Overview

EPSS Score
0.2%
Top 94% exploitable
Prevalence
Low
32-bit Linux with EROFS is a niche embedded/legacy deployment
Data Quality
6 sources
Confidence: High
EUVD NVD CVE.org EPSS MSRC Vendor VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC No
EPSS 0.2%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Defer
Exploitation· derived
None
System Exposure· derived
Small
Automatable· derived
No
Human Impact· derived
Medium

Priority Score

28
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +28
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

Same technique Information Disclosure

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CVE-2025-68613 HIGH POC
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7.5

Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise Server 16.0 Affected
SUSE Linux Enterprise Server for SAP applications 16.0 Affected
SUSE Linux Micro 6.2 Affected
SUSE Linux Micro Extras 6.2 Affected
SUSE Linux Enterprise Desktop 15 SP7 Affected

References

Advisories & patches
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-53015 ADVISORY https://ubuntu.com/security/notices/USN-8566-1 ADVISORY https://ubuntu.com/security/notices/USN-8567-1 ADVISORY https://ubuntu.com/security/notices/USN-8568-1 ADVISORY https://vuldb.com/vuln/373411 REF https://git.kernel.org/stable/c/18f9f3ddbf2ed6d245a4c6f91c51f7248f8a982c REF https://git.kernel.org/stable/c/2d8c7edcb661812249469f4a5b62e9339118846f REF https://git.kernel.org/stable/c/4fc9b12e43a3f19a01a8fb61f7961be79de20253 REF https://git.kernel.org/stable/c/582b0bf201157632cb5474c885989a6ebda46521 REF https://git.kernel.org/stable/c/858e4d98a86adf34584767388deb6c9b217f70c5 REF https://git.kernel.org/stable/c/d142250132454bf86cba87018fb2d29c482dacd6

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