CVE-2026-31535

Description

In the Linux kernel, the following vulnerability has been resolved: smb: client: make use of smbdirect_socket.recv_io.credits.available The logic off managing recv credits by counting posted recv_io and granted credits is racy. That's because the peer might already consumed a credit, but between receiving the incoming recv at the hardware and processing the completion in the 'recv_done' functions we likely have a window where we grant credits, which don't really exist. So we better have a decicated counter for the available credits, which will be incremented when we posted new recv buffers and drained when we grant the credits to the peer.

CVSS Details

CVSS Score

4.7

Severity

MEDIUM

CVSS Vector

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

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

Linux Kernel < commit 9911b1ed187a770a43950bf51f340ad4b7beecba

Linux Kernel < commit be8845ad5d6558703d20567d8702155598325db8

Linux Kernel < commit f664e6e8a81103cb45c8802a9bc7499e0902c458

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

/*
 * PoC Concept for CVE-2026-31535
 * This is a conceptual demonstration of the race condition.
 * Exploiting this requires triggering SMB Direct traffic rapidly.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

// Simulated credit counter logic (Vulnerable)
struct vulnerable_credits {
    int posted_recv;
    int granted;
};

// Simulated credit counter logic (Fixed)
struct fixed_credits {
    int available;
};

void simulate_race() {
    printf("[+] Simulating Race Condition in SMB Direct Credit Management\n");
    // In a real scenario, threads would be manipulating these counters
    // while hardware interrupts signal packet reception.
    printf("[+] Step 1: Peer consumes credit.\n");
    printf("[+] Step 2: Hardware receives packet, waits for 'recv_done'.\n");
    printf("[+] Step 3: Vulnerable logic grants credit based on stale posted_recv count.\n");
    printf("[+] Result: Credit inflation -> Resource Exhaustion/DoS.\n");
}

int main() {
    simulate_race();
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31535
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31535
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31535/
[4] VulDB https://vuldb.com/cve/CVE-2026-31535
[5] https://git.kernel.org/stable/c/9911b1ed187a770a43950bf51f340ad4b7beecba
[6] https://git.kernel.org/stable/c/be8845ad5d6558703d20567d8702155598325db8
[7] https://git.kernel.org/stable/c/f664e6e8a81103cb45c8802a9bc7499e0902c458

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31535", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-24T15:16:27.427", "lastModified": "2026-04-28T19:14:33.727", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: make use of smbdirect_socket.recv_io.credits.available\n\nThe logic off managing recv credits by counting posted recv_io and\ngranted credits is racy.\n\nThat's because the peer might already consumed a credit,\nbut between receiving the incoming recv at the hardware\nand processing the completion in the 'recv_done' functions\nwe likely have a window where we grant credits, which\ndon't really exist.\n\nSo we better have a decicated counter for the\navailable credits, which will be incremented\nwhen we posted new recv buffers and drained when\nwe grant the credits to the peer."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 4.7, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "HIGH", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.0, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-367"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.18", "versionEndExcluding": "6.18.11", "matchCriteriaId": "1D06FE45-F85F-4F59-A12C-C72C3C580DA4"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.1", "matchCriteriaId": "EE543C0D-A06B-414F-A403-CB1E088F261E"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/9911b1ed187a770a43950bf51f340ad4b7beecba", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/be8845ad5d6558703d20567d8702155598325db8", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/f664e6e8a81103cb45c8802a9bc7499e0902c458", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}