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CVE Record

CVE-2025-38638: ipv6: add a retry logic in net6_rt_notify()

In the Linux kernel, the following vulnerability has been resolved: ipv6: add a retry logic in net6_rt_notify() inet6_rt_notify() can be called under RCU protection only. This means the route could be changed concurrently and rt6_fill_node() could return -EMSGSIZE. Re-size the skb when this happens and retry, removing one WARN_ON() that syzbot was able to trigger: WARNING: CPU: 3 PID: 6291 at net/ipv6/route.c:6342 inet6_rt_notify+0x475/0x4b0 net/ipv6/route.c:6342 Modules linked in: CPU: 3 UID: 0 PID: 6291 Comm: syz.0.77 Not tainted 6.16.0-rc7-syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 RIP: 0010:inet6_rt_notify+0x475/0x4b0 net/ipv6/route.c:6342 Code: fc ff ff e8 6d 52 ea f7 e9 47 fc ff ff 48 8b 7c 24 08 4c 89 04 24 e8 5a 52 ea f7 4c 8b 04 24 e9 94 fd ff ff e8 9c fe 84 f7 90 <0f> 0b 90 e9 bd fd ff ff e8 6e 52 ea f7 e9 bb fb ff ff 48 89 df e8 RSP: 0018:ffffc900035cf1d8 EFLAGS: 00010293 RAX: 0000000000000000 RBX: ffffc900035cf540 RCX: ffffffff8a36e790 RDX: ffff88802f7e8000 RSI: ffffffff8a36e9d4 RDI: 0000000000000005 RBP: ffff88803c230f00 R08: 0000000000000005 R09: 00000000ffffffa6 R10: 00000000ffffffa6 R11: 0000000000000001 R12: 00000000ffffffa6 R13: 0000000000000900 R14: ffff888032ea4100 R15: 0000000000000000 FS: 00007fac7b89a6c0(0000) GS:ffff8880d6a20000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fac7b899f98 CR3: 0000000034b3f000 CR4: 0000000000352ef0 Call Trace: <TASK> ip6_route_mpath_notify+0xde/0x280 net/ipv6/route.c:5356 ip6_route_multipath_add+0x1181/0x1bd0 net/ipv6/route.c:5536 inet6_rtm_newroute+0xe4/0x1a0 net/ipv6/route.c:5647 rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:6944 netlink_rcv_skb+0x155/0x420 net/netlink/af_netlink.c:2552 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline] netlink_unicast+0x58d/0x850 net/netlink/af_netlink.c:1346 netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1896 sock_sendmsg_nosec net/socket.c:712 [inline] __sock_sendmsg net/socket.c:727 [inline] ____sys_sendmsg+0xa95/0xc70 net/socket.c:2566 ___sys_sendmsg+0x134/0x1d0 net/socket.c:2620

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This Linux kernel IPv6 routing bug can make route notification handling hit a kernel warning during concurrent route changes. The upstream fix resizes the netlink message buffer and retries. The sources provide no CVSS score, impact rating, or evidence of real-world exploitation, so urgency depends on how current and exposed your Linux kernel fleet is.

Executive priority

Treat this as a routine kernel hygiene item unless your environment depends heavily on IPv6 routing or runs affected 6.16-era kernels at scale. No source evidence supports emergency response or active exploitation.

Technical view

inet6_rt_notify() may run under RCU protection while IPv6 route data changes concurrently. rt6_fill_node() can return -EMSGSIZE, and the old path hit WARN_ON(). The fix retries after resizing the skb. The trace involves IPv6 multipath route addition through rtnetlink/netlink sendmsg on Linux 6.16-era kernels.

Likely exposure

Exposure appears limited to Linux systems running affected 6.16-era kernel versions with IPv6 routing functionality. The bundle lists Linux 6.16 through before 6.16.1 and 6.17 as affected, but does not provide distribution package mappings or CPEs.

Exploitation context

The source describes a syzbot-triggered WARN_ON in kernel testing. It does not state active exploitation, public weaponization, privilege requirements, or a demonstrated production impact. KEV is false in the provided bundle.

Researcher notes

Evidence is narrow: the vulnerability record and commit references describe a concurrency-triggered WARN_ON and retry fix, but not full exploitability, crash behavior, or security boundary impact. Validate against vendor kernels before assigning operational severity.

Mitigation direction

  • Identify Linux hosts running affected 6.16-era kernels.
  • Review vendor kernel advisories for backported fixes.
  • Upgrade to a kernel containing the referenced stable fixes.
  • Prioritize internet-facing or routing-heavy Linux systems first.
  • Monitor kernel logs for related IPv6 routing warnings.

Validation and detection

  • Inventory kernel versions across servers and appliances.
  • Confirm whether IPv6 routing or multipath route management is enabled.
  • Map distribution kernel builds to the upstream fix commits.
  • Check vendor changelogs for CVE-2025-38638 coverage.
  • Review logs for WARN_ON events in net/ipv6/route.c.
Prepared
Confidence
medium
Sources
4

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.

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CVE-2025-38638 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
0ADP providers
3Source links

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.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux169fd62799e8acabbfb4760799be11138ced949c, 169fd62799e8acabbfb4760799be11138ced949cunaffected
LinuxLinux6.16, 0, 6.16.1, 6.17affected
Weakness

CWE details

No CWE listed

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