{"api_version":"1","generated_at":"2026-08-22T21:53:02+00:00","cve":"CVE-2026-74656","urls":{"html":"https://cve.report/CVE-2026-74656","api":"https://cve.report/api/cve/CVE-2026-74656.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-74656","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-74656"},"summary":{"title":"ipv4: fix use-after-free in fib_nhc_update_mtu()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nipv4: fix use-after-free in fib_nhc_update_mtu()\n\nfib_nhc_update_mtu() walks the nexthop exception table under RTNL, but\nRTNL does not serialize this walk with PMTU exception updates. The walk\nuses rcu_dereference_protected() with a constant true condition without\nholding fnhe_lock.\n\nThe following interleaving can therefore occur:\n\n  CPU 0                              CPU 1\n  fib_nhc_update_mtu()               update_or_create_fnhe()\n    load fnhe                          spin_lock_bh(&fnhe_lock)\n                                       fnhe_remove_oldest()\n                                         unlink fnhe\n                                         kfree_rcu(fnhe, rcu)\n    <quiescent state>\n    access fnhe after grace period\n\nKASAN reported:\n\n  BUG: KASAN: slab-use-after-free in fib_nhc_update_mtu+0x3df/0x410\n  Read of size 8 at addr ffff888107d49000 by task poc/90\n  Call Trace:\n   fib_nhc_update_mtu+0x3df/0x410\n   fib_sync_mtu+0x7a/0xd0\n   fib_netdev_event+0x229/0x3f0\n   netif_set_mtu_ext+0x33a/0x570\n   dev_set_mtu+0x88/0x120\n\nThe same walk updates fnhe_pmtu and fnhe_mtu_locked. These fields form a\npair and other writers serialize them with fnhe_lock. RCU alone prevents\nreclamation, but would still allow concurrent writers to leave a mixed\npair.\n\nWalk the table under RCU and acquire fnhe_lock only while updating each\nexception. RCU keeps the current entry alive while the short critical\nsection serializes its paired PMTU fields. This avoids holding the global\nlock while scanning all 2048 buckets for every nexthop.","state":"PUBLISHED","assigner":"Linux","published_at":"2026-08-22 16:16:39","updated_at":"2026-08-22 16:16:39"},"problem_types":[],"metrics":[],"references":[{"url":"https://git.kernel.org/stable/c/fd39e711866498ae94fcf9acf6f422a4f045b681","name":"https://git.kernel.org/stable/c/fd39e711866498ae94fcf9acf6f422a4f045b681","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/bc5bde9ce3cc36502839dfe98e068f7303a50982","name":"https://git.kernel.org/stable/c/bc5bde9ce3cc36502839dfe98e068f7303a50982","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/ed503eaad62f20cdd5122d7c3078a648a99c8f16","name":"https://git.kernel.org/stable/c/ed503eaad62f20cdd5122d7c3078a648a99c8f16","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/e00f7d2b5f2540a3415a229c982af7a25ff6362e","name":"https://git.kernel.org/stable/c/e00f7d2b5f2540a3415a229c982af7a25ff6362e","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/5a28a4b22dde92f9d293b94236314b8d6181dc4a","name":"https://git.kernel.org/stable/c/5a28a4b22dde92f9d293b94236314b8d6181dc4a","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/63996ffc594d128ccec8fc0983f91effd2d3adc4","name":"https://git.kernel.org/stable/c/63996ffc594d128ccec8fc0983f91effd2d3adc4","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/e1e602d6b22d5cb1641c4459c487eb18bf569e0a","name":"https://git.kernel.org/stable/c/e1e602d6b22d5cb1641c4459c487eb18bf569e0a","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/dfe388da13aa784851e5ebbea90afbb099075761","name":"https://git.kernel.org/stable/c/dfe388da13aa784851e5ebbea90afbb099075761","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-74656","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-74656","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected af7d6cce53694a88d6a1bb60c9a239a6a5144459 fd39e711866498ae94fcf9acf6f422a4f045b681 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected af7d6cce53694a88d6a1bb60c9a239a6a5144459 e1e602d6b22d5cb1641c4459c487eb18bf569e0a git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected af7d6cce53694a88d6a1bb60c9a239a6a5144459 e00f7d2b5f2540a3415a229c982af7a25ff6362e git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected af7d6cce53694a88d6a1bb60c9a239a6a5144459 dfe388da13aa784851e5ebbea90afbb099075761 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 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4.19","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 4.19 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.10.265 5.10.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.15.216 5.15.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.1.183 6.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.6.152 6.6.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.12.104 6.12.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.45 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.1.9 7.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["include/net/route.h","net/ipv4/fib_semantics.c","net/ipv4/route.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"fd39e711866498ae94fcf9acf6f422a4f045b681","status":"affected","version":"af7d6cce53694a88d6a1bb60c9a239a6a5144459","versionType":"git"},{"lessThan":"e1e602d6b22d5cb1641c4459c487eb18bf569e0a","status":"affected","version":"af7d6cce53694a88d6a1bb60c9a239a6a5144459","versionType":"git"},{"lessThan":"e00f7d2b5f2540a3415a229c982af7a25ff6362e","status":"affected","version":"af7d6cce53694a88d6a1bb60c9a239a6a5144459","versionType":"git"},{"lessThan":"dfe388da13aa784851e5ebbea90afbb099075761","status":"affected","version":"af7d6cce53694a88d6a1bb60c9a239a6a5144459","versionType":"git"},{"lessThan":"5a28a4b22dde92f9d293b94236314b8d6181dc4a","status":"affected","version":"af7d6cce53694a88d6a1bb60c9a239a6a5144459","versionType":"git"},{"lessThan":"63996ffc594d128ccec8fc0983f91effd2d3adc4","status":"affected","version":"af7d6cce53694a88d6a1bb60c9a239a6a5144459","versionType":"git"},{"lessThan":"ed503eaad62f20cdd5122d7c3078a648a99c8f16","status":"affected","version":"af7d6cce53694a88d6a1bb60c9a239a6a5144459","versionType":"git"},{"lessThan":"bc5bde9ce3cc36502839dfe98e068f7303a50982","status":"affected","version":"af7d6cce53694a88d6a1bb60c9a239a6a5144459","versionType":"git"},{"status":"affected","version":"b427832009b97a3ee412ef643a80b15372a7754d","versionType":"git"},{"status":"affected","version":"2b7e4c735933be79882aba2bed9afa789e03c62f","versionType":"git"},{"status":"affected","version":"8d59c3a6376bbc6dd3f7303968a719ffba75a4f1","versionType":"git"},{"status":"affected","version":"9b4869cf385aa16f89c0f019eed4ec4e36aa441c","versionType":"git"},{"status":"affected","version":"ff34695ced21e2dfa04d0fa1c5f6c35011fa8117","versionType":"git"},{"lessThan":"3.17","status":"affected","version":"3.16.62","versionType":"semver"},{"lessThan":"4.5","status":"affected","version":"4.4.162","versionType":"semver"},{"lessThan":"4.10","status":"affected","version":"4.9.134","versionType":"semver"},{"lessThan":"4.15","status":"affected","version":"4.14.77","versionType":"semver"},{"lessThan":"4.19","status":"affected","version":"4.18.15","versionType":"semver"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["include/net/route.h","net/ipv4/fib_semantics.c","net/ipv4/route.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"4.19"},{"lessThan":"4.19","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"5.10.*","status":"unaffected","version":"5.10.265","versionType":"semver"},{"lessThanOrEqual":"5.15.*","status":"unaffected","version":"5.15.216","versionType":"semver"},{"lessThanOrEqual":"6.1.*","status":"unaffected","version":"6.1.183","versionType":"semver"},{"lessThanOrEqual":"6.6.*","status":"unaffected","version":"6.6.152","versionType":"semver"},{"lessThanOrEqual":"6.12.*","status":"unaffected","version":"6.12.104","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.45","versionType":"semver"},{"lessThanOrEqual":"7.1.*","status":"unaffected","version":"7.1.9","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.2","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.10.265","versionStartIncluding":"4.19","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.15.216","versionStartIncluding":"4.19","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.1.183","versionStartIncluding":"4.19","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.6.152","versionStartIncluding":"4.19","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.12.104","versionStartIncluding":"4.19","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.45","versionStartIncluding":"4.19","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.1.9","versionStartIncluding":"4.19","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2","versionStartIncluding":"4.19","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.16.62","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.4.162","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.9.134","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.14.77","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.18.15","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nipv4: fix use-after-free in fib_nhc_update_mtu()\n\nfib_nhc_update_mtu() walks the nexthop exception table under RTNL, but\nRTNL does not serialize this walk with PMTU exception updates. The walk\nuses rcu_dereference_protected() with a constant true condition without\nholding fnhe_lock.\n\nThe following interleaving can therefore occur:\n\n  CPU 0                              CPU 1\n  fib_nhc_update_mtu()               update_or_create_fnhe()\n    load fnhe                          spin_lock_bh(&fnhe_lock)\n                                       fnhe_remove_oldest()\n                                         unlink fnhe\n                                         kfree_rcu(fnhe, rcu)\n    <quiescent state>\n    access fnhe after grace period\n\nKASAN reported:\n\n  BUG: KASAN: slab-use-after-free in fib_nhc_update_mtu+0x3df/0x410\n  Read of size 8 at addr ffff888107d49000 by task poc/90\n  Call Trace:\n   fib_nhc_update_mtu+0x3df/0x410\n   fib_sync_mtu+0x7a/0xd0\n   fib_netdev_event+0x229/0x3f0\n   netif_set_mtu_ext+0x33a/0x570\n   dev_set_mtu+0x88/0x120\n\nThe same walk updates fnhe_pmtu and fnhe_mtu_locked. These fields form a\npair and other writers serialize them with fnhe_lock. RCU alone prevents\nreclamation, but would still allow concurrent writers to leave a mixed\npair.\n\nWalk the table under RCU and acquire fnhe_lock only while updating each\nexception. RCU keeps the current entry alive while the short critical\nsection serializes its paired PMTU fields. This avoids holding the global\nlock while scanning all 2048 buckets for every nexthop."}],"providerMetadata":{"dateUpdated":"2026-08-22T15:32:30.729Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/fd39e711866498ae94fcf9acf6f422a4f045b681"},{"url":"https://git.kernel.org/stable/c/e1e602d6b22d5cb1641c4459c487eb18bf569e0a"},{"url":"https://git.kernel.org/stable/c/e00f7d2b5f2540a3415a229c982af7a25ff6362e"},{"url":"https://git.kernel.org/stable/c/dfe388da13aa784851e5ebbea90afbb099075761"},{"url":"https://git.kernel.org/stable/c/5a28a4b22dde92f9d293b94236314b8d6181dc4a"},{"url":"https://git.kernel.org/stable/c/63996ffc594d128ccec8fc0983f91effd2d3adc4"},{"url":"https://git.kernel.org/stable/c/ed503eaad62f20cdd5122d7c3078a648a99c8f16"},{"url":"https://git.kernel.org/stable/c/bc5bde9ce3cc36502839dfe98e068f7303a50982"}],"title":"ipv4: fix use-after-free in fib_nhc_update_mtu()","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-74656","datePublished":"2026-08-22T15:32:30.729Z","dateReserved":"2026-08-15T05:44:03.923Z","dateUpdated":"2026-08-22T15:32:30.729Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-08-22 16:16:39","lastModifiedDate":"2026-08-22 16:16:39","problem_types":[],"metrics":[],"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"74656","Ordinal":"1","Title":"ipv4: fix use-after-free in fib_nhc_update_mtu()","CVE":"CVE-2026-74656","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"74656","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nipv4: fix use-after-free in fib_nhc_update_mtu()\n\nfib_nhc_update_mtu() walks the nexthop exception table under RTNL, but\nRTNL does not serialize this walk with PMTU exception updates. The walk\nuses rcu_dereference_protected() with a constant true condition without\nholding fnhe_lock.\n\nThe following interleaving can therefore occur:\n\n  CPU 0                              CPU 1\n  fib_nhc_update_mtu()               update_or_create_fnhe()\n    load fnhe                          spin_lock_bh(&fnhe_lock)\n                                       fnhe_remove_oldest()\n                                         unlink fnhe\n                                         kfree_rcu(fnhe, rcu)\n    <quiescent state>\n    access fnhe after grace period\n\nKASAN reported:\n\n  BUG: KASAN: slab-use-after-free in fib_nhc_update_mtu+0x3df/0x410\n  Read of size 8 at addr ffff888107d49000 by task poc/90\n  Call Trace:\n   fib_nhc_update_mtu+0x3df/0x410\n   fib_sync_mtu+0x7a/0xd0\n   fib_netdev_event+0x229/0x3f0\n   netif_set_mtu_ext+0x33a/0x570\n   dev_set_mtu+0x88/0x120\n\nThe same walk updates fnhe_pmtu and fnhe_mtu_locked. These fields form a\npair and other writers serialize them with fnhe_lock. RCU alone prevents\nreclamation, but would still allow concurrent writers to leave a mixed\npair.\n\nWalk the table under RCU and acquire fnhe_lock only while updating each\nexception. RCU keeps the current entry alive while the short critical\nsection serializes its paired PMTU fields. This avoids holding the global\nlock while scanning all 2048 buckets for every nexthop.","Type":"Description","Title":"ipv4: fix use-after-free in fib_nhc_update_mtu()"}]}}}