CVE-2026-31638

Description

In the Linux kernel, the following vulnerability has been resolved: rxrpc: Only put the call ref if one was acquired rxrpc_input_packet_on_conn() can process a to-client packet after the current client call on the channel has already been torn down. In that case chan->call is NULL, rxrpc_try_get_call() returns NULL and there is no reference to drop. The client-side implicit-end error path does not account for that and unconditionally calls rxrpc_put_call(). This turns a protocol error path into a kernel crash instead of rejecting the packet. Only drop the call reference if one was actually acquired. Keep the existing protocol error handling unchanged.

CVSS Details

CVSS Score

7.5

Severity

HIGH

CVSS Vector

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

Configurations (Affected Products)

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

cpe:2.3:o:linux:linux_kernel:6.2:-:*:*:*:*:*:* - VULNERABLE

Linux Kernel (Versions prior to commits 0c156aff, 6331f1b2, etc.)

PoC / Exploit Code

⚠ For Security Research Only

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

python

/*
 * Conceptual PoC for CVE-2026-31638
 * This snippet demonstrates the logic that triggers the kernel crash.
 * It requires a kernel environment with rxrpc enabled.
 */

#include <linux/module.h>
#include <linux/net.h>

// Simulated structures to represent the kernel internals
struct rxrpc_call;
struct rxrpc_channel {
    struct rxrpc_call *call;
};

// Simulate the function that fails to get the call
static inline struct rxrpc_call *rxrpc_try_get_call(struct rxrpc_call *call) {
    // In the vulnerable scenario, this returns NULL because the call is torn down
    return NULL;
}

// Simulate the function that puts the call (causes crash if NULL)
static inline void rxrpc_put_call(struct rxrpc_call *call) {
    // Missing NULL check here in the vulnerable code leads to panic
    if (call == NULL)
        panic("CVE-2026-31638: NULL pointer dereference in rxrpc_put_call");
}

void vulnerable_rxrpc_path(struct rxrpc_channel *chan) {
    struct rxrpc_call *call;

    // rxrpc_input_packet_on_conn logic
    call = rxrpc_try_get_call(chan->call);

    // Implicit-end error path
    // VULNERABILITY: The code does not check if 'call' is valid before dropping ref
    if (!call) {
        // This path is reached when processing a packet after teardown
        printk(KERN_INFO "Processing packet on torn down call...\n");
    }

    // The actual vulnerable line in the kernel source:
    // rxrpc_put_call(call); // <--- Crashes here if call is NULL
    
    // To trigger the vulnerability, an attacker sends a packet that forces
    // this execution flow with chan->call == NULL.
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31638
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31638
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31638/
[4] VulDB https://vuldb.com/cve/CVE-2026-31638
[5] https://git.kernel.org/stable/c/0c156aff8a2d4fa0d61db7837641975cf0e5452d
[6] https://git.kernel.org/stable/c/6331f1b24a3e85465f6454e003a3e6c22005a5c5
[7] https://git.kernel.org/stable/c/8299ca146489664e3c0c90a3b8900d8335b1ede4
[8] https://git.kernel.org/stable/c/9fb09861e2b8d1abfe2efaf260c9f1d30080ea38
[9] https://git.kernel.org/stable/c/b8f66447448d6c305a51413a67ec8ed26aa7d1dd

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31638", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-24T15:16:43.127", "lastModified": "2026-04-27T20:20:36.597", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nrxrpc: Only put the call ref if one was acquired\n\nrxrpc_input_packet_on_conn() can process a to-client packet after the\ncurrent client call on the channel has already been torn down. In that\ncase chan->call is NULL, rxrpc_try_get_call() returns NULL and there is\nno reference to drop.\n\nThe client-side implicit-end error path does not account for that and\nunconditionally calls rxrpc_put_call(). This turns a protocol error\npath into a kernel crash instead of rejecting the packet.\n\nOnly drop the call reference if one was actually acquired. Keep the\nexisting protocol error handling unchanged."}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-476"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2.1", "versionEndExcluding": "6.6.135", "matchCriteriaId": "D6A8AD2A-FCEB-42B6-8B79-66822D8E7C37"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.82", "matchCriteriaId": "02904CAE-71D2-45B3-9EC3-F6A9D18B6307"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.23", "matchCriteriaId": "E9E09FDD-9EE3-4A56-92E2-2B30AFD0072F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.13", "matchCriteriaId": "1490EF9B-9080-481C-8D22-1306AAE664E4"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:6.2:-:*:*:*:*:*:*", "matchCriteriaId": "3ADCCCEE-143A-4B48-9B2A-0CB97BD385DE"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*", "matchCriteriaId": "F253B622-8837-4245-BCE5-A7BF8FC76A16"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*", "matchCriteriaId": "4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*", "matchCriteriaId": "F666C8D8-6538-46D4-B318-87610DE64C34"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*", "matchCriteriaId": "02259FDA-961B-47BC-AE7F-93D7EC6E90C2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*", "matchCriteriaId": "58A9FEFF-C040-420D-8F0A-BFDAAA1DF258"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*", "matchCriteriaId": "1D2315C0-D46F-4F85-9754-F9E5E11374A6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc7:*:*:*:*:*:*", "matchCriteriaId": "512EE3A8-A590-4501-9A94-5D4B268D6138"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/0c156aff8a2d4fa0d61db7837641975cf0e5452d", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/6331f1b24a3e85465f6454e003a3e6c22005a5c5", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/8299ca146489664e3c0c90a3b8900d8335b1ede4", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/9fb09861e2b8d1abfe2efaf260c9f1d30080ea38", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/b8f66447448d6c305a51413a67ec8ed26aa7d1dd", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}