Linux Kernel up to 7.2.6/7.3-rc1 BPF bpf_timer_init use after free

Summaryinfo

A vulnerability described as very critical has been identified in Linux Kernel up to 7.2.6/7.3-rc1. This impacts the function bpf_timer_init of the component BPF. Executing a manipulation can lead to use after free. The identification of this vulnerability is CVE-2026-98033. The attack may be launched remotely. There is no exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in Linux Kernel up to 7.2.6/7.3-rc1. It has been declared as very critical. This vulnerability affects the function bpf_timer_init of the component BPF. The manipulation with an unknown input leads to a use after free vulnerability. The CWE definition for the vulnerability is CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: bpf: Preserve inner map identity in callback frames Callback frame constructors initialize map-typed argument registers with __mark_reg_known_zero() and then restore map_ptr. This clears map_uid, which is the only field distinguishing inner maps that share an inner_map_meta template. When a timer callback invokes bpf_for_each_map_elem() on a second inner map, both the saved first map and the second map value can reach the nested callback as the same template with map_uid zero. bpf_timer_init() then accepts pairing the timer from the second map with the first map. The runtime records the first map in the timer without taking a reference. Freeing that map does not find the timer stored in the second map, so a later timer callback dereferences the freed map. Copy map_uid from the same caller register as map_ptr when constructing for-each, timer/workqueue, and task-work callback arguments. The existing identity check can then reject mismatched inner maps while allowing a callback value to be paired with its actual map.

The advisory is available at git.kernel.org. This vulnerability was named CVE-2026-98033 since 09/25/2026. The exploitation appears to be easy. The attack can be initiated remotely. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $5k-$25k at the moment (estimation calculated on 09/25/2026).

Upgrading to version 7.2.7 or 7.3-rc2 eliminates this vulnerability. Applying the patch 66ff2eff093d2a0838f39c713eeb590bc0946c2a/b90c5d770dad910fb89e6c1b15052a8a1e8db752 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
• 7.3-rc1

License

• open-source

Website

• Vendor: https://www.kernel.org/

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