CVE-2025-38614: Debian Linux
Medium severity, CVSS 5.5. EPSS: 0.2% chance of exploitation in the next 30 days.
In the Linux kernel, the following vulnerability has been resolved: eventpoll: Fix semi-unbounded recursion Ensure that epoll instances can never form a graph deeper than EP_MAX_NESTS+1 links. Currently, ep_loop_check_proc() ensures that the graph is loop-free and does some recursion depth checks, but those recursion depth checks don't limit the depth of the resulting tree for two reasons: - They don't look upwards in the tree. - If there are multiple downwards paths of different lengths, only one of the paths is actually considered for the depth check since commit 28d82dc1c4ed ("epoll: limit paths"). Essentially, the current recursion depth check in ep_loop_check_proc() just serves to prevent it from recursing too deeply while checking for loops. A more thorough check is done in reverse_path_check() after the new graph edge has already been created; this checks, among other things, that no paths going upwards from any non-epoll file with a length of more than 5 edges exist. However, this check does not apply to non-epoll files. As a result, it is possible to recurse to a depth of at least roughly 500, tested on v6.15. (I am unsure if deeper recursion is possible; and this may have changed with commit 8c44dac8add7 ("eventpoll: Fix priority inversion problem").) To fix it: 1. In ep_loop_check_proc(), note the subtree depth of each visited node, and use subtree depths for the total depth calculation even when a subtree has already been visited. 2. Add ep_get_upwards_depth_proc() for similarly determining the maximum depth of an upwards walk. 3. In ep_loop_check(), use these values to limit the total path length between epoll nodes to EP_MAX_NESTS edges.
Affected products
- Debian Debian Linux: version 11.0 only
- Linux Linux Kernel: from 2.6.32.30, before 2.6.33 (fixed in 2.6.33); from 2.6.33.8, before 2.6.34 (fixed in 2.6.34); from 2.6.34.10, before 2.6.35 (fixed in 2.6.35); from 2.6.35.12, before 2.6.36 (fixed in 2.6.36); from 2.6.37.3, before 2.6.38 (fixed in 2.6.38); from 2.6.38.1, before 5.15.190 (fixed in 5.15.190); …
Published 2025-08-19. Last modified 2026-07-30.