CVE-2025-21766 (GCVE-0-2025-21766)
Vulnerability from cvelistv5
Published
2025-02-27 02:18
Modified
2026-08-05 11:54
Severity ?
8.1 (High) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ipv4: use RCU protection in __ip_rt_update_pmtu() __ip_rt_update_pmtu() must use RCU protection to make sure the net structure it reads does not disappear.
References
Impacted products
Vendor Product Version
Linux Linux Version: 2fbc6e89b2f1403189e624cabaf73e189c5e50c6
Version: 2fbc6e89b2f1403189e624cabaf73e189c5e50c6
Version: 2fbc6e89b2f1403189e624cabaf73e189c5e50c6
Version: 2fbc6e89b2f1403189e624cabaf73e189c5e50c6
Version: 2fbc6e89b2f1403189e624cabaf73e189c5e50c6
Version: 2fbc6e89b2f1403189e624cabaf73e189c5e50c6
Version: f415c264176e6095e9dee823e09c5bdd0ee0d337
Version: 98776a365da509ad923083ae54b38ee521c52742
Version: 860e2cc78c697c95bc749abb20047239fa1722ea
Version: 2b1be6c925cdf4638811765a9160796291494b89
Version: 4.14.200   ≤
Version: 4.19.148   ≤
Version: 5.4.68   ≤
Version: 5.8.12   ≤
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              "value": "AV:N - `__ip_rt_update_pmtu()` sits directly on the ICMP Fragmentation-Needed processing path \u2014 `icmp_rcv()` \u2192 `icmp_unreach()` \u2192 protocol err handlers (`udp_err`, `raw_err`, `ping_err`, `tcp_v4_err`, `ipip_err`, GRE/vti/esp/ah err) \u2192 `ipv4_sk_update_pmtu()`/`ipv4_update_pmtu()`. A remote host anywhere on the internet reaches it with a single crafted IPv4 ICMP packet, and the attacker-supplied `un.frag.mtu` becomes the value written into the FNHE entry.\nAC:H - The attacker fully controls the read side (unlimited ICMP frag-needed floods), but the freed `struct net` only becomes reachable when a namespace teardown races a long-lived cached `dst` whose `dst-\u003edev` still maps to the dying netns \u2014 network-namespace destruction and the exact preemption window between loading `dev-\u003end_net` and dereferencing it are system state a remote attacker cannot induce.\nPR:N - No authentication or credentials are involved anywhere on the path; the tunnel error handlers (`ipip_err`, GRE, vti, esp4, ah4) and `icmp_err()` dispatch on the quoted inner header alone with no socket or peer verification, so any unauthenticated host can drive `ipv4_update_pmtu()`.\nUI:N - The ICMP error is consumed entirely inside softirq packet-receive processing; no local user opens, mounts, configures, or clicks anything for the vulnerable dereference to run.\nS:U - The use-after-free read and the resulting bogus FIB lookup and FNHE writes are all confined to the kernel\u0027s own security authority; no hypervisor, IOMMU, or sandbox boundary is crossed.\nC:H - The freed `struct net` is not merely read for two sysctls \u2014 it is fed to `fib_lookup()`, which loads `net-\u003eipv4.fib_main`/`fib_default`/`rules_ops` out of reclaimed memory and walks them as FIB tables and rule lists, so a groomed reallocation of the `net_cachep` object turns this into an attacker-directed read of arbitrary kernel addresses.\nI:H - `update_or_create_fnhe()` writes through the `fib_nh_common` returned by that poisoned lookup \u2014 `rcu_assign_pointer(nhc-\u003enhc_exceptions, hash)`, `fnhe-\u003efnhe_pmtu = pmtu`, `fnhe-\u003efnhe_expires` \u2014 with `pmtu` taken verbatim from the attacker\u0027s `ntohs(icmph-\u003eun.frag.mtu)`, yielding a controlled write through a pointer chain rooted in freed memory.\nA:H - Even without weaponization, walking a FIB trie and a fib_rules list off a freed `struct net` reliably faults or corrupts state, producing a KASAN splat, oops, or panic, and the attacker can retrigger it indefinitely by replaying ICMP frag-needed packets."
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    "cveId": "CVE-2025-21766",
    "datePublished": "2025-02-27T02:18:16.570Z",
    "dateReserved": "2024-12-29T08:45:45.762Z",
    "dateUpdated": "2026-08-05T11:54:19.559Z",
    "state": "PUBLISHED"
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}


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