CVE-2026-74714
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 skipp
CSIRTS triage
- What
- BPF TCP iterator has use-after-free in batch processing loop.
- Who is affected
- Linux systems with BPF programs using tcp iterator functionality.
- Urgency
- Medium priority; risks memory corruption in BPF context.
- Action
- Apply kernel patch for bpf_iter_tcp_established_batch use-after-free.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.17% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 7% of all EPSS-scored CVEs.
Advisory coverage (2)
External references
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