# CVE-2026-74714: bpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch()

> A race condition in the Linux kernel's BPF TCP iterator allows a use-after-free, potentially enabling local attackers to execute code or escalate privileges.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** AZL-97064, BELL-CVE-2026-74714, DEBIAN-CVE-2026-74714, GHSA-cqmm-fv72-p7f7, UBUNTU-CVE-2026-74714

## What is CVE-2026-74714?

CVE-2026-74714 is a high-severity use after free vulnerability in Linux, published on 22 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

bpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch()

reqsk_queue_hash_req() publishes a TCP_NEW_SYN_RECV request_sock onto
the ehash chain, drops the bucket lock, and only afterwards sets
rsk_refcnt to 3.

Lockless readers such as __inet_lookup_established() handle this with
refcount_inc_not_zero(), but bpf_iter_tcp_established_batch() uses plain
sock_hold() while holding the bucket lock, on the assumption that the
lock guarantees sk_refcnt > 0. That assumption does not hold for
request_sock:

  CPU 0                                CPU 1
  -----                                -----
  tcp_conn_request()
   reqsk_queue_hash_req()
    inet_ehash_insert(req)
     spin_lock(bucket)
     __sk_nulls_add_node_rcu(req)      // rsk_refcnt == 0
     spin_unlock(bucket)
                                       bpf_iter_tcp_established_batch()
                                        spin_lock(bucket)
                                        sock_hold(req)   <-- addition on 0
                                        spin_unlock(bucket)
    refcount_set(&req->rsk_refcnt, 3)  // clobbers saturated value

which surfaces as:

  refcount_t: addition on 0; use-after-free.
  WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x48/0x90, CPU#1
  Call Trace:
   bpf_iter_tcp_established_batch+0x14e/0x170
   bpf_iter_tcp_batch+0x53/0x200
   bpf_iter_tcp_seq_next+0x27/0x70
   bpf_seq_read+0x107/0x410
   vfs_read+0xb9/0x380

The iterator's stolen reference is lost when the publishing CPU's
refcount_set() overwrites the count, leaving the socket one reference
short. When the last legitimate owner drops its reference the reqsk is
freed while still reachable, leading to use-after-free.

This reproduces in seconds with tcp_syncookies=0, a handful of threads
doing connect()/close() to a local listener while others read an
iter/tcp link in a tight loop.

Use refcount_inc_not_zero() and skip the socket on failure. A skipped
socket is still part of the bucket, so keep counting it in expected.
The reallocations are sized from expected, and a request sock whose
refcount gets published while the lock is held across the last realloc
must already have room.

A skipped socket is counted in expected but never batched, so end_sk
can be short of expected on a batch that is actually complete. Decide
completeness by whether the walk left any socket behind instead. The
WARN after the locked realloc checks the same, replacing an
end_sk == expected check that could not hold on that path since
commit cdec67a489d4 ("bpf: tcp: Make sure iter->batch always
contains a full bucket snapshot").

If every matching socket in a bucket is mid-init (refcount 0), end_sk
stays 0. Advance to the next bucket rather than returning a batch entry
that was never filled this round.

## Which versions are affected by CVE-2026-74714?


## How do I fix CVE-2026-74714?

Apply the vendor's patch.

## Is CVE-2026-74714 being exploited?

There is no known exploitation of CVE-2026-74714 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74714 and fix it if it is affected.

What it is: CVE-2026-74714 is a high-severity use after free vulnerability in Linux, published on 22 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-74714 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-74714/ (Markdown: https://insights.sbomify.com/CVE-2026-74714/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74714
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74714
- OSV: https://osv.dev/vulnerability/CVE-2026-74714

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74714/
Summaries are generated and may contain mistakes; the official description above is the record.