CVE-2023-52924 in Linux
Summary
by MITRE • 02/05/2025
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_tables: don't skip expired elements during walk
There is an asymmetry between commit/abort and preparation phase if the following conditions are met:
1. set is a verdict map ("1.2.3.4 : jump foo") 2. timeouts are enabled
In this case, following sequence is problematic:
1. element E in set S refers to chain C 2. userspace requests removal of set S 3. kernel does a set walk to decrement chain->use count for all elements from preparation phase 4. kernel does another set walk to remove elements from the commit phase (or another walk to do a chain->use increment for all elements from abort phase)
If E has already expired in 1), it will be ignored during list walk, so its use count won't have been changed.
Then, when set is culled, ->destroy callback will zap the element via nf_tables_set_elem_destroy(), but this function is only safe for elements that have been deactivated earlier from the preparation phase: lack of earlier deactivate removes the element but leaks the chain use count, which results in a WARN splat when the chain gets removed later, plus a leak of the nft_chain structure.
Update pipapo_get() not to skip expired elements, otherwise flush command reports bogus ENOENT errors.
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Analysis
by VulDB Data Team • 01/21/2026
The vulnerability described in CVE-2023-52924 resides within the Linux kernel's netfilter subsystem, specifically in the nf_tables component that manages network packet filtering and manipulation. This issue represents a critical inconsistency in how expired elements are handled during set operations, particularly when verdict maps with timeout functionality are involved. The flaw manifests as an asymmetry between the preparation and commit phases of set modifications, creating a scenario where elements that have already expired during the initial preparation phase are inadvertently skipped during subsequent operations, leading to improper resource management and potential system instability.
The technical root cause stems from the improper handling of expired elements during set walks, specifically when dealing with verdict maps that contain timeout mechanisms. When a set containing expired elements is being removed, the kernel performs two distinct walk operations to manage chain use counts appropriately. During the first walk in the preparation phase, expired elements are skipped due to their expired status, preventing the proper decrement of chain use counts. However, during the second walk in either the commit or abort phase, these same expired elements are processed but without the proper context of having been deactivated earlier. This creates a state where chain use counts remain inconsistent, leading to resource leaks and potential system warnings when the chain is eventually destroyed.
The operational impact of this vulnerability extends beyond simple resource leakage to potentially destabilize the kernel's networking subsystem. When the nf_tables_set_elem_destroy() function attempts to clean up elements that were never properly deactivated, it creates a scenario where the nft_chain structure remains allocated while its use count is not properly managed. This results in warning messages (WARN splats) when the chain is later removed, indicating improper reference counting and resource management. The vulnerability also affects flush commands, which may incorrectly report ENOENT errors due to the pipapo_get() function skipping expired elements during lookup operations, creating false negatives in administrative operations.
This vulnerability aligns with CWE-457: Use of Uninitialized Variable and CWE-691: Insufficient Control Flow Management, as it demonstrates improper handling of element lifecycle management within the netfilter framework. The issue also maps to ATT&CK technique T1547.001: Registry Run Keys / Startup Folder, though indirectly, as improper kernel resource management can create persistent system instability that may affect system startup processes. The flaw represents a classic case of improper state management where the kernel fails to maintain consistent accounting of resource references across different phases of transaction processing. The fix requires ensuring that expired elements are not skipped during set walks to maintain proper chain use count management and prevent resource leaks that could lead to system instability or denial of service conditions.