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CVE Record

CVE-2023-53477: ipv6: Add lwtunnel encap size of all siblings in nexthop calculation

In the Linux kernel, the following vulnerability has been resolved: ipv6: Add lwtunnel encap size of all siblings in nexthop calculation In function rt6_nlmsg_size(), the length of nexthop is calculated by multipling the nexthop length of fib6_info and the number of siblings. However if the fib6_info has no lwtunnel but the siblings have lwtunnels, the nexthop length is less than it should be, and it will trigger a warning in inet6_rt_notify() as follows: WARNING: CPU: 0 PID: 6082 at net/ipv6/route.c:6180 inet6_rt_notify+0x120/0x130 ...... Call Trace: <TASK> fib6_add_rt2node+0x685/0xa30 fib6_add+0x96/0x1b0 ip6_route_add+0x50/0xd0 inet6_rtm_newroute+0x97/0xa0 rtnetlink_rcv_msg+0x156/0x3d0 netlink_rcv_skb+0x5a/0x110 netlink_unicast+0x246/0x350 netlink_sendmsg+0x250/0x4c0 sock_sendmsg+0x66/0x70 ___sys_sendmsg+0x7c/0xd0 __sys_sendmsg+0x5d/0xb0 do_syscall_64+0x3f/0x90 entry_SYSCALL_64_after_hwframe+0x72/0xdc This bug can be reproduced by script: ip -6 addr add 2002::2/64 dev ens2 ip -6 route add 100::/64 via 2002::1 dev ens2 metric 100 for i in 10 20 30 40 50 60 70; do ip link add link ens2 name ipv_$i type ipvlan ip -6 addr add 2002::$i/64 dev ipv_$i ifconfig ipv_$i up done for i in 10 20 30 40 50 60; do ip -6 route append 100::/64 encap ip6 dst 2002::$i via 2002::1 dev ipv_$i metric 100 done ip -6 route append 100::/64 via 2002::1 dev ipv_70 metric 100 This patch fixes it by adding nexthop_len of every siblings using rt6_nh_nlmsg_size().

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2023-53477 is a Linux kernel IPv6 routing bug. Certain complex IPv6 route configurations with lightweight tunnel encapsulation can cause the kernel to miscalculate netlink message size and trigger a kernel warning. Public sources do not provide a CVSS score or evidence of active exploitation.

Executive priority

Treat as a routine kernel maintenance issue unless the environment relies heavily on Linux IPv6 routing. Prioritize network infrastructure and hosts where untrusted users or containers can influence route configuration.

Technical view

The flaw is in rt6_nlmsg_size() for IPv6 route notifications. It calculated nexthop length from one fib6_info times sibling count, missing lwtunnel encapsulation sizes on siblings. The upstream fix sums each sibling using rt6_nh_nlmsg_size().

Likely exposure

Systems running affected Linux kernels with IPv6 routing features enabled are potentially exposed, especially routers, hosts using ipvlan, lwtunnel encapsulation, or complex IPv6 multipath routes. Practical triggering appears to require route-management capability, not unauthenticated network access.

Exploitation context

The CVE record includes a local configuration-based reproducer that triggers a kernel warning. There is no KEV listing and no cited evidence of active exploitation. Public sources do not establish privilege impact beyond the warning condition.

Researcher notes

The public description is precise about the faulty size calculation and fix direction, but lacks CVSS, CWE, and distribution-specific affected ranges. Avoid assuming remote exploitability; the provided reproducer requires administrative network configuration operations.

Mitigation direction

  • Apply Linux kernel updates that include the referenced stable fixes.
  • Check distribution advisories for backported fixes and affected package versions.
  • Limit route-management privileges to trusted administrators and controlled automation.
  • Review use of IPv6 lwtunnel, ipvlan, and multipath route configurations.

Validation and detection

  • Inventory Linux kernel versions across IPv6-capable systems.
  • Confirm vendor kernel packages include one of the referenced stable commits or equivalent backport.
  • Review kernel logs for IPv6 route warning traces near inet6_rt_notify().
  • Prioritize validation on routers and systems managing dynamic IPv6 routes.
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

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-2023-53477 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
7Source 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
LinuxLinuxbeb1afac518dec5a15dc92ba8f0ca016dcf457b4, beb1afac518dec5a15dc92ba8f0ca016dcf457b4, beb1afac518dec5a15dc92ba8f0ca016dcf457b4, beb1afac518dec5a15dc92ba8f0ca016dcf457b4, beb1afac518dec5a15dc92ba8f0ca016dcf457b4, beb1afac518dec5a15dc92ba8f0ca016dcf457b4unaffected
LinuxLinux4.11, 0, 5.4.235, 5.10.173, 5.15.100, 6.1.18, 6.2.5, 6.3affected
Weakness

CWE details

No CWE listed

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