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CVE Record

CVE-2024-40905: ipv6: fix possible race in __fib6_drop_pcpu_from()

In the Linux kernel, the following vulnerability has been resolved: ipv6: fix possible race in __fib6_drop_pcpu_from() syzbot found a race in __fib6_drop_pcpu_from() [1] If compiler reads more than once (*ppcpu_rt), second read could read NULL, if another cpu clears the value in rt6_get_pcpu_route(). Add a READ_ONCE() to prevent this race. Also add rcu_read_lock()/rcu_read_unlock() because we rely on RCU protection while dereferencing pcpu_rt. [1] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000012: 0000 [#1] PREEMPT SMP KASAN PTI KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097] CPU: 0 PID: 7543 Comm: kworker/u8:17 Not tainted 6.10.0-rc1-syzkaller-00013-g2bfcfd584ff5 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024 Workqueue: netns cleanup_net RIP: 0010:__fib6_drop_pcpu_from.part.0+0x10a/0x370 net/ipv6/ip6_fib.c:984 Code: f8 48 c1 e8 03 80 3c 28 00 0f 85 16 02 00 00 4d 8b 3f 4d 85 ff 74 31 e8 74 a7 fa f7 49 8d bf 90 00 00 00 48 89 f8 48 c1 e8 03 <80> 3c 28 00 0f 85 1e 02 00 00 49 8b 87 90 00 00 00 48 8b 0c 24 48 RSP: 0018:ffffc900040df070 EFLAGS: 00010206 RAX: 0000000000000012 RBX: 0000000000000001 RCX: ffffffff89932e16 RDX: ffff888049dd1e00 RSI: ffffffff89932d7c RDI: 0000000000000091 RBP: dffffc0000000000 R08: 0000000000000005 R09: 0000000000000007 R10: 0000000000000001 R11: 0000000000000006 R12: ffff88807fa080b8 R13: fffffbfff1a9a07d R14: ffffed100ff41022 R15: 0000000000000001 FS: 0000000000000000(0000) GS:ffff8880b9200000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000001b32c26000 CR3: 000000005d56e000 CR4: 00000000003526f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> __fib6_drop_pcpu_from net/ipv6/ip6_fib.c:966 [inline] fib6_drop_pcpu_from net/ipv6/ip6_fib.c:1027 [inline] fib6_purge_rt+0x7f2/0x9f0 net/ipv6/ip6_fib.c:1038 fib6_del_route net/ipv6/ip6_fib.c:1998 [inline] fib6_del+0xa70/0x17b0 net/ipv6/ip6_fib.c:2043 fib6_clean_node+0x426/0x5b0 net/ipv6/ip6_fib.c:2205 fib6_walk_continue+0x44f/0x8d0 net/ipv6/ip6_fib.c:2127 fib6_walk+0x182/0x370 net/ipv6/ip6_fib.c:2175 fib6_clean_tree+0xd7/0x120 net/ipv6/ip6_fib.c:2255 __fib6_clean_all+0x100/0x2d0 net/ipv6/ip6_fib.c:2271 rt6_sync_down_dev net/ipv6/route.c:4906 [inline] rt6_disable_ip+0x7ed/0xa00 net/ipv6/route.c:4911 addrconf_ifdown.isra.0+0x117/0x1b40 net/ipv6/addrconf.c:3855 addrconf_notify+0x223/0x19e0 net/ipv6/addrconf.c:3778 notifier_call_chain+0xb9/0x410 kernel/notifier.c:93 call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:1992 call_netdevice_notifiers_extack net/core/dev.c:2030 [inline] call_netdevice_notifiers net/core/dev.c:2044 [inline] dev_close_many+0x333/0x6a0 net/core/dev.c:1585 unregister_netdevice_many_notify+0x46d/0x19f0 net/core/dev.c:11193 unregister_netdevice_many net/core/dev.c:11276 [inline] default_device_exit_batch+0x85b/0xae0 net/core/dev.c:11759 ops_exit_list+0x128/0x180 net/core/net_namespace.c:178 cleanup_net+0x5b7/0xbf0 net/core/net_namespace.c:640 process_one_work+0x9fb/0x1b60 kernel/workqueue.c:3231 process_scheduled_works kernel/workqueue.c:3312 [inline] worker_thread+0x6c8/0xf70 kernel/workqueue.c:3393 kthread+0x2c1/0x3a0 kernel/kthread.c:389 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel IPv6 routing race found by syzbot. Under specific cleanup timing, the kernel can dereference a cleared per-CPU route pointer and crash. The sources show it has been fixed upstream, but they do not provide CVSS, attack prerequisites, or evidence of real-world exploitation.

Executive priority

Handle as a patch-management item with uncertain severity. It can crash affected Linux kernels, but the bundle does not show active exploitation or business-impacting attack details. Prioritize based on kernel exposure, multi-tenant workload risk, and vendor advisory relevance.

Technical view

The flaw is in __fib6_drop_pcpu_from() in Linux IPv6 FIB cleanup. A second compiler read of *ppcpu_rt could observe NULL after another CPU clears it in rt6_get_pcpu_route(). The fix adds READ_ONCE() and RCU read-side protection while dereferencing pcpu_rt.

Likely exposure

Exposure is limited to systems running affected Linux kernel versions or downstream products that include them. The affected context is IPv6 routing cleanup, including network namespace and device teardown paths. The bundle does not prove whether exploitation requires local privileges, namespace access, or specific configuration.

Exploitation context

The source bundle reports a syzbot-triggered kernel oops and says KEV is false. No cited source in the bundle reports active exploitation, public weaponization, or a practical attack path. Treat exploitability evidence as incomplete.

Researcher notes

Key uncertainty is triggerability outside syzkaller. The crash path involves cleanup_net, addrconf_ifdown, rt6_disable_ip, and fib6 route deletion. The fix is a race hardening change: READ_ONCE plus RCU read locking around pcpu_rt dereference.

Mitigation direction

  • Upgrade to a kernel or vendor package containing the referenced upstream stable fix.
  • Follow downstream vendor guidance for Debian LTS and Siemens affected products.
  • Prioritize internet-facing and multi-tenant Linux hosts after confirming kernel exposure.
  • Avoid direct wrangler-style assumptions; validate through vendor advisories and package changelogs.
  • Monitor kernel crash logs for IPv6 FIB cleanup oops signatures until patched.

Validation and detection

  • Inventory running kernel versions across Linux servers, containers hosts, and appliances.
  • Compare versions against the affected ranges and referenced stable commits.
  • Check package changelogs for CVE-2024-40905 or the IPv6 pcpu route race fix.
  • Review logs for __fib6_drop_pcpu_from, fib6_purge_rt, or IPv6 route cleanup crashes.
  • Confirm applicable Debian LTS or Siemens advisories for managed products.
Prepared
Confidence
medium
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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CVE-2024-40905 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
3ADP providers
12Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CVECVE Program Container
CISA-ADPCISA ADP Vulnrichment
other:ssvc
siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxd52d3997f843ffefaa8d8462790ffcaca6c74192, d52d3997f843ffefaa8d8462790ffcaca6c74192, d52d3997f843ffefaa8d8462790ffcaca6c74192, d52d3997f843ffefaa8d8462790ffcaca6c74192, d52d3997f843ffefaa8d8462790ffcaca6c74192, d52d3997f843ffefaa8d8462790ffcaca6c74192, d52d3997f843ffefaa8d8462790ffcaca6c74192unaffected
LinuxLinux4.2, 0, 5.4.279, 5.10.221, 5.15.162, 6.1.95, 6.6.35, 6.9.6, 6.10affected
Weakness

CWE details

No CWE listed

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