CVE-2026-74714: Software Security Vulnerability Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-cqmm-fv72-p7f7",
  "modified" : "2026-08-25T06:31:30Z",
  "published" : "2026-08-22T18:30:30Z",
  "aliases" : [ "CVE-2026-74714" ],
  "details" : "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch()\n\nreqsk_queue_hash_req() publishes a TCP_NEW_SYN_RECV request_sock onto\nthe ehash chain, drops the bucket lock, and only afterwards sets\nrsk_refcnt to 3.\n\nLockless readers such as __inet_lookup_established() handle this with\nrefcount_inc_not_zero(), but bpf_iter_tcp_established_batch() uses plain\nsock_hold() while holding the bucket lock, on the assumption that the\nlock guarantees sk_refcnt > 0. That assumption does not hold for\nrequest_sock:\n\n  CPU 0                                CPU 1\n  -----                                -----\n  tcp_conn_request()\n   reqsk_queue_hash_req()\n    inet_ehash_insert(req)\n     spin_lock(bucket)\n     __sk_nulls_add_node_rcu(req)      // rsk_refcnt == 0\n     spin_unlock(bucket)\n                                       bpf_iter_tcp_established_batch()\n                                        spin_lock(bucket)\n                                        sock_hold(req)   <-- addition on 0\n                                        spin_unlock(bucket)\n    refcount_set(&req->rsk_refcnt, 3)  // clobbers saturated value\n\nwhich surfaces as:\n\n  refcount_t: addition on 0; use-after-free.\n  WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x48/0x90, CPU#1\n  Call Trace:\n   bpf_iter_tcp_established_batch+0x14e/0x170\n   bpf_iter_tcp_batch+0x53/0x200\n   bpf_iter_tcp_seq_next+0x27/0x70\n   bpf_seq_read+0x107/0x410\n   vfs_read+0xb9/0x380\n\nThe iterator's stolen reference is lost when the publishing CPU's\nrefcount_set() overwrites the count, leaving the socket one reference\nshort. When the last legitimate owner drops its reference the reqsk is\nfreed while still reachable, leading to use-after-free.\n\nThis reproduces in seconds with tcp_syncookies=0, a handful of threads\ndoing connect()/close() to a local listener while others read an\niter/tcp link in a tight loop.\n\nUse refcount_inc_not_zero() and skip the socket on failure. A skipped\nsocket is still part of the bucket, so keep counting it in expected.\nThe reallocations are sized from expected, and a request sock whose\nrefcount gets published while the lock is held across the last realloc\nmust already have room.\n\nA skipped socket is counted in expected but never batched, so end_sk\ncan be short of expected on a batch that is actually complete. Decide\ncompleteness by whether the walk left any socket behind instead. The\nWARN after the locked realloc checks the same, replacing an\nend_sk == expected check that could not hold on that path since\ncommit cdec67a489d4 (\"bpf: tcp: Make sure iter->batch always\ncontains a full bucket snapshot\").\n\nIf every matching socket in a bucket is mid-init (refcount 0), end_sk\nstays 0. Advance to the next bucket rather than returning a batch entry\nthat was never filled this round.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-74714"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/7d2b60a4bc0499f62ff8520af6309bbe170882fd"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/97e74d3e45d653c07c2d406fc530a9bbe3df8396"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/cc0295f89296ed351fc4b0b48fee887ba02c5d24"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/cefcbbe20846a45f9a7dae868f7ef1000953e2df"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/ddbe966b5d1fe212ada749bc3d0b410f1a7dea74"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/e5fd3f514e27db1f05fbd72ba615d74941e23c51"
  } ],
  "database_specific" : {
    "cwe_ids" : [ ],
    "severity" : "HIGH",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-08-22T16:16:46Z"
  }
}