Cloudanix VulnDB

CVE-2026-98503

None

CVSS

—

EPSS

0.2%

Published

Oct 18, 2026

CISA due date

—

Cloudanix analysis

Schedule a fix SSVC: Track

A flaw in the Linux kernel's handling of network packet rings could let a local user corrupt memory or crash the system by racing the reuse of packet buffers.

Exploitation
Local Privilege
Attacker needs
Low Privilege
Complexity
Moderate
Impact
Privilege Gain
Component
OS kernel
Class
Race Condition
Remediation
Upgrade
Effort
Medium
Patch risk
Low

What it actually does

Race condition in AF_PACKET TX_RING allows ring slots to be released and reused while an skb still holds references to the payload via destructor or orphan paths, enabling aliasing of in-flight packet state.

Why it matters to the business

Local attackers can trigger memory corruption or crashes in network transmit paths on affected Linux systems, potentially leading to denial of service or kernel-level compromise; low public exploitability but high severity for multi-tenant or exposed packet socket workloads.

How an attack unfolds

An attacker with local access creates a TX_RING, sends skbs that reference ring slots, then forces early skb_orphan or skb_orphan_frags_rx calls to release the slot before transmission completes, allowing reuse of the slot for malicious data while the original skb still points to it.

How to fix it

Apply the upstream kernel patch that switches to ubuf_info completion callbacks and allocates per-packet tpacket_uarg; rebuild and reboot into a fixed kernel version. Monitor for backports to stable branches.

How to confirm the fix worked

Confirm the presence of the ubuf_info completion path and removal of the pg_vec test in tpacket_destruct_skb; test by exercising TX_RING transmit paths under skb_orphan conditions and verify no premature slot release occurs.

Typical attack path

  1. Obtain local unprivileged access on a system using AF_PACKET sockets
  2. Allocate a TX_RING and populate slots with packet data
  3. Transmit packets while triggering skb_orphan paths via socket operations or network stack events
  4. Reuse the now-freed slot with attacker-controlled data before the original skb is fully released
  5. Trigger use-after-free or aliasing to corrupt kernel structures or escalate privileges

How to detect it

Review kernel logs for AF_PACKET ring-related warnings or oopses during transmit; inspect process activity creating packet sockets and performing rapid ring operations; correlate with any unexpected skb destructor behavior in ftrace or perf captures.

What your security team should do

  • Prioritize patching kernel packages on systems that expose AF_PACKET to untrusted users or containers
  • Restrict CAP_NET_RAW and packet socket usage via seccomp or LSM policies where possible
  • Monitor EPSS and exploit maturity for any increase in public tooling

The record

In the Linux kernel, the following vulnerability has been resolved: packet: use ubuf_info completion for TX_RING packets tpacket_snd sends skbs with frags pointing into its ring slots. Slots are released when skb->destructor is called. A call to skb_orphan calls skb->destructor before the skb is freed. This can cause the slot to be reused while still linked into the skb. Switch to standard zerocopy completion (ubuf_info) so the slot is only released once all references to the payload are freed or copied. Restore skb->destructor to standard sock_wfree. The ubuf_info completion callback can be called with a NULL skb, but only from net_zcopy_put and related API, used by zerocopy implementations that hold their own reference on the uarg, such as MSG_ZEROCOPY. This uarg is only ever completed from skb_zcopy_clear, so skb is always set. To prevent userspace from aliasing in-flight state on shared ring slots, allocate tpacket_uarg per packet, rather than per slot. This adds a small allocation to the transmit path. Use standard kmalloc to allow backporting to stable kernels. The uarg holds an sk_wmem_alloc reference, rather than an sk_refcnt reference. packet_free_tx_ring waits on sk_wmem_alloc before freeing the ring pages. Always allocate vec->deferred for tx_ring so page-backed rings also wait on sk_wmem_alloc when skb_copy_ubufs drops page refs before calling tpacket_ubuf_complete. Drop the tx_ring.pg_vec test that tpacket_destruct_skb performed before accessing the slot. The sk_wmem_alloc reference now guarantees that the slot is valid. The test is also not sufficient by itself, as it reads pg_vec without pg_vec_lock, so it can race with packet_set_ring. As a result a slot is released when its payload is copied, which can be before transmission (e.g., in skb_orphan_frags_rx). If copied before skb_tx_timestamp() is called, no slot timestamp is recorded, similar to when skb_orphan() was called early in the datapath before this patch. Revert the now unused previous skb_zcopy_.._nouarg infra. Depends on commit 992cc9f94ca9 ("net/packet: defer vmalloc TX_RING free until skbs finish").

Affected packages

Ecosystem Package Introduced Fixed