EUVD-2026-64593
GHSA-4hv8-gc9j-4wjf
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Race condition exploitation requires precise multi-core timing between MTU events and RCU grace period completion, warranting AC:H over the vendor-assigned AC:L; all other metrics match the local, low-privilege, full-kernel-impact nature of the flaw.
Primary rating from Vendor (Linux).
CVSS VectorVendor: Linux
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Lifecycle Timeline
5DescriptionCVE.org
In the Linux kernel, the following vulnerability has been resolved:
ipv4: fix use-after-free in fib_nhc_update_mtu()
fib_nhc_update_mtu() walks the nexthop exception table under RTNL, but RTNL does not serialize this walk with PMTU exception updates. The walk uses rcu_dereference_protected() with a constant true condition without holding fnhe_lock.
The following interleaving can therefore occur:
CPU 0 CPU 1 fib_nhc_update_mtu() update_or_create_fnhe() load fnhe spin_lock_bh(&fnhe_lock) fnhe_remove_oldest() unlink fnhe kfree_rcu(fnhe, rcu) <quiescent state> access fnhe after grace period
KASAN reported:
BUG: KASAN: slab-use-after-free in fib_nhc_update_mtu+0x3df/0x410 Read of size 8 at addr ffff888107d49000 by task poc/90 Call Trace: fib_nhc_update_mtu+0x3df/0x410 fib_sync_mtu+0x7a/0xd0 fib_netdev_event+0x229/0x3f0 netif_set_mtu_ext+0x33a/0x570 dev_set_mtu+0x88/0x120
The same walk updates fnhe_pmtu and fnhe_mtu_locked. These fields form a pair and other writers serialize them with fnhe_lock. RCU alone prevents reclamation, but would still allow concurrent writers to leave a mixed pair.
Walk the table under RCU and acquire fnhe_lock only while updating each exception. RCU keeps the current entry alive while the short critical section serializes its paired PMTU fields. This avoids holding the global lock while scanning all 2048 buckets for every nexthop.
AnalysisAI
Use-after-free race condition in the Linux kernel's IPv4 routing subsystem allows a local low-privileged user to corrupt kernel memory and potentially escalate privileges to root. The flaw is in fib_nhc_update_mtu(), which traverses the PMTU nexthop exception (FNHE) table without proper serialization against concurrent FNHE eviction, creating a window where freed memory is accessed after a completed RCU grace period. …
Unlock full vulnerability intelligence
- Risk assessment & exploitation conditions
- Attack chain visualization
- Remediation with exact patch versions
- Threat intelligence from 22 sources
- Personal watchlist & email alerts
Free forever · No credit card required
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires a local account with sufficient privilege to trigger MTU changes on a network interface - a low-privileged user account (PR:L per CVSS) is sufficient, as standard Linux users can open network sockets that drive PMTU updates. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 score of 7.8 (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) captures the local privilege escalation ceiling correctly, but the AC:L designation understates practical exploitation difficulty: triggering the race requires precise interleaving between an MTU change event and a concurrent PMTU exception eviction, which is inherently timing-sensitive and more consistent with AC:H in most environments. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | A local, low-privileged attacker on a multi-core Linux host repeatedly induces MTU changes on a network interface (e.g., via repeated 'ip link set dev eth0 mtu' calls) while simultaneously generating network traffic that triggers PMTU exception updates. On a second CPU, fib_nhc_update_mtu() loads a pointer to an fnhe that update_or_create_fnhe() concurrently unlinks and schedules for RCU reclamation. … |
| Remediation | The primary remediation is upgrading to a patched kernel release: 5.10.265, 5.15.216, 6.1.183, 6.6.152, 6.12.104, 6.18.45, 7.1.9, or 7.2 and later. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify all Linux systems in your environment and document their current kernel versions, prioritizing production servers and systems with multiple user accounts. …
Sign in for detailed remediation steps and compensating controls.
Threat intelligence, references, and detailed analysis are available after sign-in.
Same technique Information Disclosure
View allShare
External POC / Exploit Code
Leaving vuln.today