Linux: Use After Free
CVE-2025-38248 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 5df2d582f6e8a81e7ab066464845b38b2fb04094, 7bb080340bb5ffc928f47c563a9ca1528ce54911, 4d3c2a1d4c7c33103f1ddfdbc5cfe1ea4f6d0dcd as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.31% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to 5df2d582f6e8a81e7ab066464845b38b2fb04094 or 7bb080340bb5ffc928f47c563a9ca1528ce54911 or 4d3c2a1d4c7c33103f1ddfdbc5cfe1ea4f6d0dcd or bdced577da71b118b6ed4242ebd47f81bf54d406, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.15.5 or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 2796d846d74a18cc6563e96eff8bf28c5e06f912 up to, but not including, 5df2d582f6e8a81e7ab066464845b38b2fb04094; 2796d846d74a18cc6563e96eff8bf28c5e06f912 up to, but not including, 7bb080340bb5ffc928f47c563a9ca1528ce54911; 2796d846d74a18cc6563e96eff8bf28c5e06f912 up to, but not including, 4d3c2a1d4c7c33103f1ddfdbc5cfe1ea4f6d0dcd; 2796d846d74a18cc6563e96eff8bf28c5e06f912 up to, but not including, bdced577da71b118b6ed4242ebd47f81bf54d406; 2796d846d74a18cc6563e96eff8bf28c5e06f912 up to, but not including, f05a4f9e959e0fc098046044c650acf897ea52d2; 2796d846d74a18cc6563e96eff8bf28c5e06f912 up to, but not including, 7544f3f5b0b58c396f374d060898b5939da31709; 5.15 | 5df2d582f6e8a81e7ab066464845b38b2fb04094, 7bb080340bb5ffc928f47c563a9ca1528ce54911, 4d3c2a1d4c7c33103f1ddfdbc5cfe1ea4f6d0dcd, bdced577da71b118b6ed4242ebd47f81bf54d406, f05a4f9e959e0fc098046044c650acf897ea52d2, 7544f3f5b0b58c396f374d060898b5939da31709 |
| Linux | Linux Kernel | 5.15 up to, but not including, 6.15.5; 6.16 | 6.15.5 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA |
| CVSS 3.1 | 7.8 | High | NVD |
Official description
In the Linux kernel, the following vulnerability has been resolved: bridge: mcast: Fix use-after-free during router port configuration The bridge maintains a global list of ports behind which a multicast router resides. The list is consulted during forwarding to ensure multicast packets are forwarded to these ports even if the ports are not member in the matching MDB entry. When per-VLAN multicast snooping is enabled, the per-port multicast context is disabled on each port and the port is removed from the global router port list: # ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1 # ip link add name dummy1 up master br1 type dummy # ip link set dev dummy1 type bridge_slave mcast_router 2 $ bridge -d mdb show | grep router router ports on br1: dummy1 # ip link set dev br1 type bridge mcast_vlan_snooping 1 $ bridge -d mdb show | grep router However, the port can be re-added to the global list even when per-VLAN multicast snooping is enabled: # ip link set dev dummy1 type bridge_slave mcast_router 0 # ip link set dev dummy1 type bridge_slave mcast_router 2 $ bridge -d mdb show | grep router router ports on br1: dummy1 Since commit 4b30ae9adb04 ("net: bridge: mcast: re-implement br_multicast_{enable, disable}_port functions"), when per-VLAN multicast snooping is enabled, multicast disablement on a port will disable the per-{port, VLAN} multicast contexts and not the per-port one. As a result, a port will remain in the global router port list even after it is deleted. This will lead to a use-after-free [1] when the list is traversed (when adding a new port to the list, for example): # ip link del dev dummy1 # ip link add name dummy2 up master br1 type dummy # ip link set dev dummy2 type bridge_slave mcast_router 2 Similarly, stale entries can also be found in the per-VLAN router port list. When per-VLAN multicast snooping is disabled, the per-{port, VLAN} contexts are disabled on each port and the port is removed from the per-VLAN router port list: # ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1 mcast_vlan_snooping 1 # ip link add name dummy1 up master br1 type dummy # bridge vlan add vid 2 dev dummy1 # bridge vlan global set vid 2 dev br1 mcast_snooping 1 # bridge vlan set vid 2 dev dummy1 mcast_router 2 $ bridge vlan global show dev br1 vid 2 | grep router router ports: dummy1 # ip link set dev br1 type bridge mcast_vlan_snooping 0 $ bridge vlan global show dev br1 vid 2 | grep router However, the port can be re-added to the per-VLAN list even when per-VLAN multicast snooping is disabled: # bridge vlan set vid 2 dev dummy1 mcast_router 0 # bridge vlan set vid 2 dev dummy1 mcast_router 2 $ bridge vlan global show dev br1 vid 2 | grep router router ports: dummy1 When the VLAN is deleted from the port, the per-{port, VLAN} multicast context will not be disabled since multicast snooping is not enabled on the VLAN. As a result, the port will remain in the per-VLAN router port list even after it is no longer member in the VLAN. This will lead to a use-after-free [2] when the list is traversed (when adding a new port to the list, for example): # ip link add name dummy2 up master br1 type dummy # bridge vlan add vid 2 dev dummy2 # bridge vlan del vid 2 dev dummy1 # bridge vlan set vid 2 dev dummy2 mcast_router 2 Fix these issues by removing the port from the relevant (global or per-VLAN) router port list in br_multicast_port_ctx_deinit(). The function is invoked during port deletion with the per-port multicast context and during VLAN deletion with the per-{port, VLAN} multicast context. Note that deleting the multicast router timer is not enough as it only takes care of the temporary multicast router states (1 or 3) and not the permanent one (2). [1] BUG: KASAN: slab-out-of-bounds in br_multicast_add_router.part.0+0x3f1/0x560 Write of size 8 at addr ffff888004a67328 by task ip/384 [...] Call Trace: <TASK> dump_stack ---truncated---
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other references
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