Answer in brief
CVE-2026-74656 records a High severity (CVSS 7.8) vulnerability in ipv4: fix use-after-free in fib_nhc_update_mtu(). The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <fd39e711866498ae94fcf9acf6f422a4f045b681 || >=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <e1e602d6b22d5cb1641c4459c487eb18bf569e0a || >=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <e00f7d2b5f2540a3415a229c982af7a25ff6362e || >=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <dfe388da13aa784851e5ebbea90afbb099075761 || >=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <5a28a4b22dde92f9d293b94236314b8d6181dc4a || >=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <63996ffc594d128ccec8fc0983f91effd2d3adc4 || >=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <ed503eaad62f20cdd5122d7c3078a648a99c8f16 || >=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <bc5bde9ce3cc36502839dfe98e068f7303a50982 || b427832009b97a3ee412ef643a80b15372a7754d || 2b7e4c735933be79882aba2bed9afa789e03c62f || 8d59c3a6376bbc6dd3f7303968a719ffba75a4f1 || 9b4869cf385aa16f89c0f019eed4ec4e36aa441c || ff34695ced21e2dfa04d0fa1c5f6c35011fa8117 || >=3.16.62 <3.17 || >=4.4.162 <4.5 || >=4.9.134 <4.10 || >=4.14.77 <4.15 || >=4.18.15 <4.19 | fd39e711866498ae94fcf9acf6f422a4f045b681, e1e602d6b22d5cb1641c4459c487eb18bf569e0a, e00f7d2b5f2540a3415a229c982af7a25ff6362e, dfe388da13aa784851e5ebbea90afbb099075761, 5a28a4b22dde92f9d293b94236314b8d6181dc4a, 63996ffc594d128ccec8fc0983f91effd2d3adc4, ed503eaad62f20cdd5122d7c3078a648a99c8f16, bc5bde9ce3cc36502839dfe98e068f7303a50982, 3.17, 4.5, 4.10, 4.15, 4.19 |
| Linux/Linuxgeneric | 4.19 | Not reported |
Published upstream
Aug 22, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 25, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 22, 2026
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.
Quoted source text, attributed separately from HOL analysis.