VulnerabilityPublished 24 Apr 2026Updated 19 Oct 2026

CVE-2026-31539: Linux kernel · smb: smbdirect: introduce smbdirect_socket.recv_io.credits.available

Affects Linux kernelSource CVE Database V5

Not known to be exploited · CVSS 7.5 High · fixed in f99996870222b598914a1f49d7375dc23752c237 : patch Linux kernel soon.

Data as of 26 Oct 2026, 14:18 UTC

CVSS 3.1 base score

7.5High

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

EPSS

0.3% chance of exploitation in 30 days – higher than 25% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation: No evidence of active exploitation and no public proof of concept
Automatable: Attackers can reliably automate steps 1–4 of the kill chain
Technical impact: Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-10-16.

Patch

Available – fixed in f99996870222b598914a1f49d7375dc23752c237, e811e60e1cc79923c4388146eb1fa26a7482731e, 6e3c5052f9686192e178806e017b7377155f4bab

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
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: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
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 24 Apr 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.

What to do

Upgrade Linux kernel to f99996870222b598914a1f49d7375dc23752c237, e811e60e1cc79923c4388146eb1fa26a7482731e or 6e3c5052f9686192e178806e017b7377155f4bab.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 5fb9b459b3686e366640edd4e62805ef7b4de927, < f99996870222b598914a1f49d7375dc23752c237	Fixed in f99996870222b598914a1f49d7375dc23752c237
LinuxLinux	Affected ≥ 5fb9b459b3686e366640edd4e62805ef7b4de927, < e811e60e1cc79923c4388146eb1fa26a7482731e	Fixed in e811e60e1cc79923c4388146eb1fa26a7482731e
LinuxLinux	Affected ≥ 5fb9b459b3686e366640edd4e62805ef7b4de927, < 6e3c5052f9686192e178806e017b7377155f4bab	Fixed in 6e3c5052f9686192e178806e017b7377155f4bab
LinuxLinux	Affected =6.18	Fixed in–

AI-suggested

A fix is available and has been applied in the Linux kernel commits identified by hashes f99996870222b598914a1f49d7375dc23752c237, e811e60e1cc79923c4388146eb1fa26a7482731e, and 6e3c5052f9686192e178806e017b7377155f4bab. Users should update to a Linux kernel version that includes these fixes to remediate the vulnerability.

Description

CVE-2026-31539 is a race condition vulnerability in the Linux kernel's smb smbdirect component related to the management of receive credits. The flaw arises because the logic counting posted receive IO and granted credits can become inconsistent, potentially granting credits that do not exist. This issue has been addressed by introducing a dedicated counter for available credits to ensure accurate tracking.

Impact

The vulnerability can cause a race condition that affects the availability of receive credits in the smb smbdirect socket communication. While the CVSS score indicates no confidentiality or integrity impact, it has a high impact on availability, potentially leading to denial of service conditions in affected Linux kernel versions.

Summary

This vulnerability in the Linux kernel affects the smb smbdirect subsystem's receive credit management. The original logic counted posted receive IO and granted credits in a way that was racy, allowing a window where credits could be granted to a peer that were not actually available. The fix introduces a dedicated counter, smbdirect_socket.recv_io.credits.available, which increments when new receive buffers are posted and decrements when credits are granted, eliminating the race condition.

CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') (opens in a new tab)
Class weaknessLikelihood of exploit: MediumOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
Architecture and Design
In languages that support it, use synchronization primitives. Only wrap these around critical code to minimize the impact on performance.
Architecture and Design
Use thread-safe capabilities such as the data access abstraction in Spring.
Architecture and Design
Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
Secure Design Principles (opens in a new tab)
OWASP ASVS 4.0.3
V1.11.2 (opens in a new tab)
Attack patterns
Leveraging Time-of-Check and Time-of-Use (TOCTOU) Race Conditions (opens in a new tab)
Leveraging Race Conditions (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Oct 2026, 13:58 UTC

WeaknessesCWE-362

Technical details

References

Community reviews

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