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CVE Record

CVE-2026-23124: ipv6: annotate data-race in ndisc_router_discovery()

In the Linux kernel, the following vulnerability has been resolved: ipv6: annotate data-race in ndisc_router_discovery() syzbot found that ndisc_router_discovery() could read and write in6_dev->ra_mtu without holding a lock [1] This looks fine, IFLA_INET6_RA_MTU is best effort. Add READ_ONCE()/WRITE_ONCE() to document the race. Note that we might also reject illegal MTU values (mtu < IPV6_MIN_MTU || mtu > skb->dev->mtu) in a future patch. [1] BUG: KCSAN: data-race in ndisc_router_discovery / ndisc_router_discovery read to 0xffff888119809c20 of 4 bytes by task 25817 on cpu 1: ndisc_router_discovery+0x151d/0x1c90 net/ipv6/ndisc.c:1558 ndisc_rcv+0x2ad/0x3d0 net/ipv6/ndisc.c:1841 icmpv6_rcv+0xe5a/0x12f0 net/ipv6/icmp.c:989 ip6_protocol_deliver_rcu+0xb2a/0x10d0 net/ipv6/ip6_input.c:438 ip6_input_finish+0xf0/0x1d0 net/ipv6/ip6_input.c:489 NF_HOOK include/linux/netfilter.h:318 [inline] ip6_input+0x5e/0x140 net/ipv6/ip6_input.c:500 ip6_mc_input+0x27c/0x470 net/ipv6/ip6_input.c:590 dst_input include/net/dst.h:474 [inline] ip6_rcv_finish+0x336/0x340 net/ipv6/ip6_input.c:79 ... write to 0xffff888119809c20 of 4 bytes by task 25816 on cpu 0: ndisc_router_discovery+0x155a/0x1c90 net/ipv6/ndisc.c:1559 ndisc_rcv+0x2ad/0x3d0 net/ipv6/ndisc.c:1841 icmpv6_rcv+0xe5a/0x12f0 net/ipv6/icmp.c:989 ip6_protocol_deliver_rcu+0xb2a/0x10d0 net/ipv6/ip6_input.c:438 ip6_input_finish+0xf0/0x1d0 net/ipv6/ip6_input.c:489 NF_HOOK include/linux/netfilter.h:318 [inline] ip6_input+0x5e/0x140 net/ipv6/ip6_input.c:500 ip6_mc_input+0x27c/0x470 net/ipv6/ip6_input.c:590 dst_input include/net/dst.h:474 [inline] ip6_rcv_finish+0x336/0x340 net/ipv6/ip6_input.c:79 ... value changed: 0x00000000 -> 0xe5400659

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2026-23124 is a Linux kernel IPv6 neighbor-discovery data race found by syzbot. The source says the race involves router-advertisement MTU handling and was resolved by annotating reads and writes. No business impact, CVSS score, or exploitation evidence is provided.

Executive priority

Treat this as a normal kernel maintenance item, not an emergency, unless your vendor assigns higher severity or your environment has sensitive IPv6 exposure.

Technical view

The issue is a concurrent read/write of in6_dev->ra_mtu in ndisc_router_discovery() without locking. The kernel fix uses READ_ONCE()/WRITE_ONCE() to document and control the data race. The source notes IFLA_INET6_RA_MTU is best effort and mentions possible future validation of illegal MTU values.

Likely exposure

Exposure is limited to Linux systems running affected kernel builds with IPv6 neighbor discovery enabled. The bundle lists Linux kernel versions/lines including 5.15 through 6.19, but distro package mapping requires vendor advisories.

Exploitation context

No active exploitation is indicated. The CVE is not marked KEV, and the source bundle only describes syzbot/KCSAN detection of a kernel data race, not attacker use or a public exploit.

Researcher notes

Evidence is narrow: a KCSAN-reported data race in IPv6 router discovery, resolved by READ_ONCE()/WRITE_ONCE(). No CVSS, CWE, crash impact, privilege boundary, or exploitability claim is present in the bundle.

Mitigation direction

  • Check your Linux distribution advisory for CVE-2026-23124 package mapping.
  • Update kernels to vendor builds containing the referenced stable fixes.
  • Prioritize internet-adjacent IPv6 infrastructure after vendor impact confirmation.
  • Track vendor guidance if MTU validation changes in a future patch.

Validation and detection

  • Inventory Linux kernel versions across servers, appliances, and cloud images.
  • Confirm whether IPv6 is enabled on exposed network interfaces.
  • Map installed distro kernel packages to the vendor’s fixed release.
  • Review kernel changelogs for the referenced ndisc_router_discovery fix.
Prepared
Confidence
medium
Sources
8

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

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ATT&CK lookup starting points

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CVE-2026-23124 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
1ADP providers
7Source 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

CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7, 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7, 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7, 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7, 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7, 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7unaffected
LinuxLinux5.15, 0, 5.15.199, 6.1.162, 6.6.122, 6.12.68, 6.18.8, 6.19affected
Weakness

CWE details

No CWE listed

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