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Linux Kernel CVE-2026-53391

| EUVDEUVD-2026-45513 HIGH
NULL Pointer Dereference (CWE-476)
2026-07-19 Linux GHSA-72jx-g4pr-67hm
Denial Of Service Linux Null Pointer Dereference
7.5
CVSS 3.1 · Vendor: Linux
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Attack ChainAIDerived

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

  1. Access
    Compromise or impersonate NFS metadata server
  2. Delivery
    Client mounts pNFS flexfiles share
  3. Exploit
    Client issues GETDEVICEINFO request
  4. Execution
    Server returns zero-length r_addr netaddr4
  5. Persist
    Decoder calls strrchr on NULL buffer
  6. Impact
    Kernel NULL deref panics client

Vulnerability Assessment

Weakness
CWE
CWE-476
OWASP Top 10:2025
A10:2025 - Mishandling of Exceptional Conditions
ASVS 5.0
V16 - Security Logging and Error Handling Null pointer safety, defensive checks
MITRE ATT&CK

1 technique across 1 tactic: Impact

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

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Exploitation Conditions

Exploitation requires the target to be a Linux NFSv4.1+/pNFS client using the flexfiles layout driver, and requires the attacker to control, compromise, or impersonate the NFS metadata server the client mounts from; the trigger is a GETDEVICEINFO multipath-DS response carrying a zero-length r_addr (or r_netid) netaddr4 opaque, which the client requests when resolving data-server addresses. Despite PR:N in the CVSS vector, exploitation is limited to environments that actually deploy pNFS flexfiles and mount against a server outside their trust boundary - clients that never use pNFS flexfiles, or that only mount trusted metadata servers, are not realistically reachable. No client-side authentication or user interaction beyond an existing/attempted NFS mount is needed, and the attack is a single malformed server response.
Impact

The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H, base 7.5) captures a network-reachable, low-complexity, unauthenticated availability-only impact, which aligns with the description: only integrity/confidentiality are untouched (C:N/I:N) and the outcome is a client crash (A:H). However, the raw score understates an important trust prerequisite that the vector cannot express: the victim client must have voluntarily mounted a pNFS-flexfile NFSv4 share against the attacker-controlled or compromised metadata server. This is a server-to-client attack, not an arbitrary internet-facing exploit, so PR:N is technically correct (the server holds no credentials on the client) but real-world reachability is gated by NFS topology. EPSS is low (0.17%, 7th percentile) and there is no KEV listing and no public exploit, all consistent with a niche, targeted risk rather than widespread opportunistic exploitation. This is a genuine reliability/availability bug worth patching on NFS clients using pNFS flexfiles, but it is not a drop-everything internet-exposed RCE - priority should scale with whether an environment actually mounts pNFS flexfiles from servers outside its trust boundary. No conflicting signals were found; the CVSS availability focus, the DoS tag, and the description all agree.
Exploit ScenarioDerived

An attacker who controls or has compromised an NFS metadata server (or can man-in-the-middle unauthenticated NFS traffic) waits for a Linux pNFS-flexfile client to issue a GETDEVICEINFO request, then replies with a multipath-DS body whose r_addr opaque has length zero. When the client decodes the response, strrchr is called on a NULL buffer and the kernel panics, taking down the client host. No public proof-of-concept is identified at this time, and the low complexity (AC:L) means a single crafted response suffices.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.2% exploitation probability (EPSS)

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AnalysisAIv1 – Jul 20, 2026

Remote denial of service in the Linux kernel's NFSv4/pNFS flexfiles client allows a malicious or compromised NFS metadata server to crash any mounted client by returning a GETDEVICEINFO response containing a zero-length r_addr or r_netid opaque. The decoder nfs4_decode_mp_ds_addr() only checks for negative lengths, so a zero-length value leaves the buffer pointer NULL and the subsequent strrchr(NULL, '.') triggers a kernel NULL-pointer dereference and panic. There is no public exploit identified at time of analysis, and EPSS is low (0.17%, 7th percentile), consistent with a targeted server-side trust attack rather than mass exploitation.

RemediationAI

Vendor-released patch: update to a fixed stable kernel - 5.15.211, 6.1.177, 6.6.144, 6.12.95, 6.18.38, 7.1.3, or mainline 7.2-rc1 (or later), which add explicit zero-length rejection returning -EBADMSG. Apply your distribution's kernel security update as the primary fix and reboot; the patched commits are available at git.kernel.org/stable/c/76b94cbd32aacf36a641956385a852635c6802b9 and the sibling stable commits in the references. Where immediate patching is not possible, the concrete compensating control is to avoid or restrict use of pNFS flexfiles: mount NFS with a layout type that avoids the flexfiles device-info path, or ensure clients only mount pNFS from trusted, controlled metadata servers within your security boundary (network-restrict or firewall client access so it cannot reach untrusted NFS metadata servers). The trade-off is that disabling pNFS flexfiles removes the parallel-I/O performance benefit for those mounts, and network restrictions may complicate legitimate multi-server NFS deployments. Consult the advisory at https://nvd.nist.gov/vuln/detail/CVE-2026-53391 and vuldb.com/vuln/380126 for tracking.

Affected VersionsENISA

Linux 6b7f3cf96364eaf597940cb5c68a682894829915 <012d37a568bfbb2c9686f03ade75560bc7139956
Linux patch: 7.1.3
Linux patch: 6.12.95
Linux patch: 6.6.144
Linux 6b7f3cf96364eaf597940cb5c68a682894829915 <30aae62e50b4e074a90a9a5e15246548fbdc1182
Linux patch: 7.2-rc1
Linux 6b7f3cf96364eaf597940cb5c68a682894829915 <76b94cbd32aacf36a641956385a852635c6802b9
Linux patch: 5.15.211
Linux 4.0
Linux 6b7f3cf96364eaf597940cb5c68a682894829915 <427ab81a811dab4bca9d19f82eec5847ae42646e
Linux patch: 6.18.38
Linux 6b7f3cf96364eaf597940cb5c68a682894829915 <41fe0f7b84f0cb822ae10ab08592996a592b2a25
Linux 6b7f3cf96364eaf597940cb5c68a682894829915 <c8e4e0c701d0192a2efb6df059c0f9e19678c23d
Linux patch: 6.1.177
Linux 6b7f3cf96364eaf597940cb5c68a682894829915 <6c344fff2feff9d4d716d8e4ad40e9b5040ee5ea
Linux patch: 0

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

The flaw lives in the pNFS (parallel NFS) flexfiles layout driver within the Linux kernel NFSv4 client. When a client requests device information (GETDEVICEINFO) for a multipath data server, the server returns a netaddr4 structure containing r_netid (transport identifier, e.g. 'tcp') and r_addr (the IP/port string). Both fields are decoded with xdr_stream_decode_string_dup(), which for a zero-length on-wire opaque falls through to setting *str = NULL and returning 0. The code guarded only against a negative return ('nlen < 0' / 'rlen < 0'), so a legitimate-looking zero-length field slips past and the very next operation, strrchr(buf, '.') to find the port separator, dereferences NULL. The root cause class is CWE-476 (NULL Pointer Dereference); the input CWE field is marked N/A but the description unambiguously describes a NULL deref. The fix rejects zero-length cases explicitly, returning -EBADMSG so the malformed body is handled gracefully instead of panicking.

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Severity by source

Vendor (Linux) PRIMARY 7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
vuln.today AI 7.5 HIGH

Server-to-client crash needs no client credentials (PR:N) and a single crafted response (AC:L, AV:N); only availability is impacted (A:H), C/I:N, with no scope change.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE 6.2 MEDIUM
AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Red Hat 7.0 MEDIUM

Primary rating from Vendor (Linux).

CVSS VectorVendor: Linux

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

Lifecycle Timeline

4
CVSS changed
Jul 20, 2026 - 15:22 NVD
7.5 (HIGH)
Patch available
Jul 19, 2026 - 14:17 EUVD
CVE Published
Jul 19, 2026 - 12:01 cve.org
UNKNOWN (no severity yet)
CVE Published
Jul 19, 2026 - 12:01 cve.org
HIGH 7.5

DescriptionCVE.org

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

NFSv4/pNFS: reject zero-length r_addr in nfs4_decode_mp_ds_addr

nfs4_decode_mp_ds_addr() decodes the r_netid and r_addr opaques of a netaddr4 from a GETDEVICEINFO multipath-DS body, then immediately calls strrchr(buf, '.') to locate the port separator. Both decodes use xdr_stream_decode_string_dup(), and the current code checks only "nlen < 0" / "rlen < 0" before dereferencing the returned string.

When the on-wire opaque has length zero, xdr_stream_decode_opaque_inline() returns 0 and xdr_stream_decode_string_dup() falls through to its "*str = NULL; return ret" tail, leaving buf NULL with a return value of 0. The "< 0" check does not catch this, and the next line is strrchr(NULL, '.'), a kernel NULL pointer dereference reachable from any pNFS-flexfile client mounted against a malicious or compromised metadata server.

Reject the zero-length cases explicitly so the decoder fails with -EBADMSG (treated as a malformed GETDEVICEINFO body) instead of panicking the client.

Executive ViewAI

Why It Matters

CVE-2026-53391 enables storage infrastructure compromise to cascade into production system failures: a single malicious or compromised NFS server can remotely crash all connected client systems. Organizations using shared NFS storage face widespread service disruption if their storage infrastructure is breached. A patch is available and should be deployed urgently to prevent infrastructure-wide outages.

Business Impact: High
Compensating Controls

Apply vendor patch.

Threat Intelligence Overview

EPSS Score
0.2%
Top 93% exploitable
Prevalence
Ubiquitous
Linux kernel is ubiquitous, though the vulnerable pNFS-flexfiles client path is niche
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 HIGH
CISA KEV No
Public POC No
EPSS 0.2%
Patch available Yes
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
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
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
Yes
Human Impact
High

Priority Score

38
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +38
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Null Pointer Dereference MEDIUM

A null pointer dereference occurs when a program attempts to access memory through a pointer that has been set to NULL (address 0x0).

Denial of Service MEDIUM

Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.

Same weakness CWE-476 – NULL Pointer Dereference

View all
CVE-2016-0742 HIGH
7.5
CVE-2014-3470 MEDIUM
4.3
CVE-2020-1967 HIGH POC
7.5
CVE-2017-3730 HIGH POC
7.5
CVE-2017-3169 CRITICAL POC
9.8
CVE-2016-4957 HIGH
7.5
CVE-2021-3449 MEDIUM
5.9
CVE-2015-3194 HIGH
7.5

Same technique Denial Of Service

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CVE-2015-5119 CRITICAL POC
9.8
CVE-2011-2462 CRITICAL POC
9.8
CVE-2011-0611 HIGH POC
8.8
CVE-2012-1889 HIGH POC
8.8
CVE-2012-0507 CRITICAL POC
9.8
CVE-2014-1761 HIGH POC
7.8
CVE-2015-5122 CRITICAL POC
9.8
CVE-2011-0609 HIGH POC
7.8

Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Availability Extension 15 SP7 Affected
SUSE Linux Enterprise High Availability Extension 15 SP7 Affected

References

Advisories & patches
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-53391 ADVISORY https://seclists.org/oss-sec/2026/q3/230 ADVISORY https://ubuntu.com/security/notices/USN-8726-1 ADVISORY https://ubuntu.com/security/notices/USN-8727-1 ADVISORY https://vuldb.com/vuln/380126 REF https://git.kernel.org/stable/c/012d37a568bfbb2c9686f03ade75560bc7139956 REF https://git.kernel.org/stable/c/30aae62e50b4e074a90a9a5e15246548fbdc1182 REF https://git.kernel.org/stable/c/41fe0f7b84f0cb822ae10ab08592996a592b2a25 REF https://git.kernel.org/stable/c/427ab81a811dab4bca9d19f82eec5847ae42646e REF https://git.kernel.org/stable/c/6c344fff2feff9d4d716d8e4ad40e9b5040ee5ea REF https://git.kernel.org/stable/c/76b94cbd32aacf36a641956385a852635c6802b9 REF https://git.kernel.org/stable/c/c8e4e0c701d0192a2efb6df059c0f9e19678c23d

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