CVE-2026-74656: linux
Vulnerability summary
CVE-2026-74656 is a high (CVSS 7.8) vulnerability in linux. EPSS estimates a 0.13% chance of exploitation in the next 30 days, higher than 2% of scored vulnerabilities.
Advisory lineage
Upstream 0 · Downstream 7 · Related 6Timeline
- 22-08-2026PublishedVulnerability first disclosed.
- 16-10-2026Last modifiedVulnerability information updated.
Description
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.
CVSS metrics
4 scores · 4 sources · 1 version- OSV · UbuntuEcosystem advisory · calculated7.8HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- OSV · DebianEcosystem advisory · calculated7.8HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- NVDNIST7.8HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS trend
Probability
0.13%
Chance of exploitation in the next 30 days
Percentile
2%
Versus all other CVEs
30-day change
0.00 pp
From 0.13% on 19-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeNo weakness data has been published for this record.
Affected systems
Ubuntu169 products
- linuxAll versions (No fix recorded) | < 5.15.0-198.208
- linux-allwinner-5.19All versions (No fix recorded)
- linux-awsAll versions (No fix recorded) | < 5.15.0-1117.124
- linux-aws-5.0All versions (No fix recorded)
- linux-aws-5.11All versions (No fix recorded)
Debian2 products
- linux< 6.1.187-1 | < 6.12.105-1 | < 7.1.9-1
- linux-6.12< 6.12.107-1~deb12u1
Linux1 product
- linux≥ 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 | 4.19
3 vendors · 172 products
