CVE-2024-26924 netfilter: nft_set_pipapo: do not free live element
A use-after-free vulnerability in the Linux kernel netfilter subsystem allows attackers to cause a system crash via crafted network filter rules.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-26924?
CVE-2024-26924 is a high-severity use after free vulnerability in Debian Debian Linux, published on 24 Apr 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nft_set_pipapo: do not free live element
Pablo reports a crash with large batches of elements with a back-to-back add/remove pattern. Quoting Pablo:
add_elem("00000000") timeout 100 ms ... add_elem("0000000X") timeout 100 ms del_elem("0000000X") <---------------- delete one that was just added ... add_elem("00005000") timeout 100 ms
1) nft_pipapo_remove() removes element 0000000X Then, KASAN shows a splat.
Looking at the remove function there is a chance that we will drop a rule that maps to a non-deactivated element.
Removal happens in two steps, first we do a lookup for key k and return the to-be-removed element and mark it as inactive in the next generation. Then, in a second step, the element gets removed from the set/map.
The _remove function does not work correctly if we have more than one element that share the same key.
This can happen if we insert an element into a set when the set already holds an element with same key, but the element mapping to the existing key has timed out or is not active in the next generation.
In such case its possible that removal will unmap the wrong element. If this happens, we will leak the non-deactivated element, it becomes unreachable.
The element that got deactivated (and will be freed later) will remain reachable in the set data structure, this can result in a crash when such an element is retrieved during lookup (stale pointer).
Add a check that the fully matching key does in fact map to the element that we have marked as inactive in the deactivation step. If not, we need to continue searching.
Add a bug/warn trap at the end of the function as well, the remove function must not ever be called with an invisible/unreachable/non-existent element.
v2: avoid uneeded temporary variable (Stefano)
Weakness: CWE-476
Which versions are affected by CVE-2024-26924?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2024-26924?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2024-26924 being exploited?
There is no known exploitation of CVE-2024-26924 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as BELL-CVE-2024-26924, DEBIAN-CVE-2024-26924, GHSA-6vh7-f36j-r556, UBUNTU-CVE-2024-26924, USN-6863-1.