CVE-2026-98021
Received Received - Intake

Linux Kernel tx_queue_len Integer Overflow Fix

Publication date: 2026-09-25

Last updated on: 2026-09-25

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: net: reject oversized tx_queue_len at netlink parse time rtnl_create_link() assigns IFLA_TXQLEN directly to dev->tx_queue_len without going through netif_change_tx_queue_len(), so a device created with "ip link add ... txqueuelen 500000" bypasses the S16_MAX cap and still triggers the oversized ring allocations in pfifo_fast, tun and tap. The veth peer nest (rtnl_nla_parse_ifinfomsg()) and the RTM_NEWLINK-on-existing-device path reach the same sinks. Enforce the cap in ifla_policy instead: IFLA_TXQLEN becomes NLA_POLICY_FULL_RANGE(NLA_U32, &txqlen_range) with txqlen_range = { .min = 0, .max = S16_MAX }. All netlink consumers parse against this policy - rtnl_setlink(), rtnl_newlink() (create and change), and the veth peer nest - so every netlink path is capped at parse time and rejects the attribute with -ERANGE plus a proper "integer out of range" extack message before any device state is modified (the RTM_SETLINK half-application wart is gone with it). Document the bound in the rt-link.yaml netlink spec. Conditions to recreate the bug: - CONFIG_NET_SCHED=y, CONFIG_VETH=y, CONFIG_USER_NS=y, CONFIG_NET_NS=y. - Unprivileged user in a fresh user+net namespace (unshare -Urn): ip link add v0 txqueuelen 500000 type veth peer name v1 -> on the fixed kernel this is rejected with -ERANGE ("integer out of range" extack) instead of installing an oversized tx_queue_len that later inflates pfifo_fast/tun/tap ring allocations. - ip link set v0 txqueuelen 500000 is likewise rejected at parse time.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published
2026-09-25
Last Modified
2026-09-25
Generated
2026-09-25
AI Q&A
2026-09-25
EPSS Evaluated
N/A
NVD
CVE-2026-98021
EUVD
EUVD-2026-86674

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

Helpful Resources

Exploitability

CWE
CWE Icon
KEV
KEV Icon
CWE ID Description
CWE-UNKNOWN

Attack-Flow Graph

AI Quick Actions

Instant insights powered by AI
Executive Summary

This vulnerability in the Linux kernel allows an unprivileged user to set an excessively large tx_queue_len value (e.g., 500000) when creating or modifying network devices via netlink. This bypasses the S16_MAX cap and triggers oversized ring allocations in components like pfifo_fast, tun, and tap, potentially causing memory exhaustion or system instability.

Detection Guidance

To detect this vulnerability, check if any network device has an excessively large tx_queue_len value. Run: ip link show. Look for values exceeding S16_MAX (32767). If any device shows a txqueuelen larger than this, it may be vulnerable.

Impact Analysis

An attacker could exploit this to cause denial-of-service by allocating excessive memory for network device queues, leading to system crashes or resource exhaustion. It requires specific kernel configurations and unprivileged user access in a fresh namespace.

Mitigation Strategies

Update your Linux kernel to a patched version that enforces the tx_queue_len cap. If you cannot update immediately, manually set tx_queue_len to a safe value (e.g., 1000) using: ip link set dev <device> txqueuelen 1000.

Chat Assistant

Ask questions about this CVE
Hi! I’m here to help you understand CVE-2026-98021. Ask me anything about the vulnerability, its impact, or mitigation strategies.
0/70

EPSS Chart