VulnerabilityPublished 19 Jul 2026Updated 29 Jul 2026

CVE-2026-53393: Linux kernel · nfsd: reset write verifier on deferred writeback errors

Source GCVE Database

Not known to be exploited · CVSS 5.5 Medium.

Data as of 26 Oct 2026, 12:55 UTC

CVSS 3.1 base score

5.5Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 2% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 19 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-wm3m-j54f-523v

What to do

AI-suggested

A fix has been implemented in the Linux kernel to reset the write verifier on deferred writeback errors in the nfsd server code. Users should apply the official kernel updates that include this patch to ensure correct handling of writeback errors and prevent silent data loss. Patch status is not explicitly stated in the provided data; check the vendor or kernel advisory for the exact fixed versions and update accordingly.

Description

A vulnerability in the Linux kernel's NFS server (nfsd) was resolved involving the handling of deferred writeback errors. The issue was that the server's write verifier was not reset when certain writeback errors occurred, causing clients to incorrectly believe their data was durably stored when it was not. This violates the durability guarantees of the NFS protocol. The fix involves adding calls to reset the write verifier on these error paths.

Impact

Clients using NFS with UNSTABLE writes may incorrectly assume their data has been durably stored after a COMMIT operation, despite underlying writeback failures. This can lead to silent data loss, violating the durability guarantees of the NFS protocol. There is no impact on confidentiality or integrity, but availability (data durability) is affected.

Summary

The Linux kernel NFS server functions nfsd_vfs_write() and nfsd_commit() failed to rotate the server's write verifier (nn->writeverf) upon detecting deferred writeback errors via filemap_check_wb_err(). This omission meant that clients holding UNSTABLE write data could commit and receive the unchanged verifier, falsely concluding their data was durable and silently losing data that failed writeback. The vulnerability violates the UNSTABLE+COMMIT durability contract defined in RFC 1813 §3.3.7 and RFC 8881 §18.32. The patch adds commit_reset_write_verifier() calls at the error sites to ensure the verifier is rotated, matching other durable-storage-failure paths and preventing silent data loss.

References

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