Linux Kernel up to 7.2.7/7.3-rc3 Netlink /proc/net/netlink netlink_realloc_groups buffer overflow

Summaryinfo

A vulnerability has been found in Linux Kernel up to 7.2.7/7.3-rc3 and classified as very critical. This issue affects the function netlink_realloc_groups of the file /proc/net/netlink of the component Netlink. Performing a manipulation of the argument groups results in buffer overflow. This vulnerability is known as CVE-2026-98284. Remote exploitation of the attack is possible. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability, which was classified as very critical, was found in Linux Kernel up to 7.2.7/7.3-rc3. This affects the function netlink_realloc_groups of the file /proc/net/netlink of the component Netlink. The manipulation of the argument groups with an unknown input leads to a buffer overflow vulnerability. CWE is classifying the issue as CWE-120. The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: netlink: do not free nlk->groups while lockless readers can use it netlink_realloc_groups() uses krealloc() under netlink_table_grab(). Whenever NLGRPSZ(groups) lands in a different kmalloc bucket, the old bitmap is freed immediately. Two readers of nlk->groups / nlk->ngroups do not hold the netlink table lock: 1) sk_diag_dump_groups(). Hashed (bound) sockets are dumped from the rhashtable walk in __netlink_diag_dump(), which only holds RCU. Only the mc_list part of the dump takes nl_table_lock. 2) netlink_native_seq_show() (/proc/net/netlink), whose walk has been lockless since commit 21e4902aea80 ("netlink: Lockless lookup with RCU grace period in socket release"). Both can read a freed buffer, and sk_diag_dump_groups() can also read past the end of the old (smaller) buffer if it happens to load the old @groups pointer together with the new @ngroups value, copying the result into a NETLINK_DIAG_GROUPS attribute. This is the same class of bug that commit f773608026ee ("netlink: access nlk groups safely in netlink bind and getname") fixed for bind() and getname(); these two readers were missed. Simply grabbing the table lock in sk_diag_dump_groups() is not an option, because it is also called with nl_table_lock already held from the mc_list section of the dump. Make the lockless readers safe instead: - Allocate a new bitmap and free the old one after an RCU grace period, instead of relying on the implicit kfree() done by krealloc(). - Publish @groups before @ngroups, both with release semantics, and have the lockless readers load @ngroups first. A reader can then never pair the new (bigger) size with the old (smaller) buffer, and a reader picking up the new pointer while still seeing the old size is guaranteed to see the initialized bitmap. netlink_realloc_groups() is called from process context (bind() and setsockopt()), so kfree_rcu_mightsleep() can be used, once the table has been released.

The advisory is shared at git.kernel.org. This vulnerability is uniquely identified as CVE-2026-98284 since 09/25/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. Technical details are known, but no exploit is available. The price for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 10/06/2026).

Upgrading to version 7.2.8 or 7.3-rc4 eliminates this vulnerability. Applying the patch 22f313e211d58a66786c81487c3905fa5d4b2a8f/ceac0de741bfb47ca255eee075257b3bb31f0651 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5
• 7.2.6
• 7.2.7
• 7.3-rc1
• 7.3-rc2
• 7.3-rc3

License

• open-source

Website

• Vendor: https://www.kernel.org/

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