VulnerabilityPublished 25 Mar 2026Updated 5 Nov 2026

CVE-2026-23300: Linux kernel · net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop

Affects Linux kernelSource CVE Database V5

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Not known to be exploited · fixed in f7c9f8e3607440fe39300efbaf46cf7b5eecb23f : update Linux kernel when convenient.

Data as of 5 Nov 2026, 22:04 UTC

Severity

Unrated

Rated by Threat Radar · No CVSS score from NVD or the CNA

Thin evidence

One scorer or none

Exploitation: No evidence of active exploitation and no public proof of concept
Automatable: Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact: Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-11-05.

Patch

Available – fixed in f7c9f8e3607440fe39300efbaf46cf7b5eecb23f, c11d7c56c2076ee9cd72004f1976fe0734df2ae9, b299121e7453d23faddf464087dff513a495b4fc +5

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 493ced1ac47c48bb86d9d4e8e87df8592be85a0e, < f7c9f8e3607440fe39300efbaf46cf7b5eecb23f	Fixed in f7c9f8e3607440fe39300efbaf46cf7b5eecb23f
LinuxLinux	Affected ≥ 493ced1ac47c48bb86d9d4e8e87df8592be85a0e, < c11d7c56c2076ee9cd72004f1976fe0734df2ae9	Fixed in c11d7c56c2076ee9cd72004f1976fe0734df2ae9
LinuxLinux	Affected ≥ 493ced1ac47c48bb86d9d4e8e87df8592be85a0e, < b299121e7453d23faddf464087dff513a495b4fc	Fixed in b299121e7453d23faddf464087dff513a495b4fc
LinuxLinux	Affected ≥ 493ced1ac47c48bb86d9d4e8e87df8592be85a0e, < b5062fc2150614c9ea8a611c2e0cb6e047ebfa3a	Fixed in b5062fc2150614c9ea8a611c2e0cb6e047ebfa3a
LinuxLinux	Affected ≥ 493ced1ac47c48bb86d9d4e8e87df8592be85a0e, < b3b5a037d520afe3d5276e653bc0ff516bbda34c	Fixed in b3b5a037d520afe3d5276e653bc0ff516bbda34c
LinuxLinux	Affected ≥ 493ced1ac47c48bb86d9d4e8e87df8592be85a0e, < 8650db85b4259d2885d2a80fbc2317ce24194133	Fixed in 8650db85b4259d2885d2a80fbc2317ce24194133

Description

In the Linux kernel, the following vulnerability has been resolved: net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop When a standalone IPv6 nexthop object is created with a loopback device (e.g., "ip -6 nexthop add id 100 dev lo"), fib6_nh_init() misclassifies it as a reject route. This is because nexthop objects have no destination prefix (fc_dst=::), causing fib6_is_reject() to match any loopback nexthop. The reject path skips fib_nh_common_init(), leaving nhc_pcpu_rth_output unallocated. If an IPv4 route later references this nexthop, __mkroute_output() dereferences NULL nhc_pcpu_rth_output and panics. Simplify the check in fib6_nh_init() to only match explicit reject routes (RTF_REJECT) instead of using fib6_is_reject(). The loopback promotion heuristic in fib6_is_reject() is handled separately by ip6_route_info_create_nh(). After this change, the three cases behave as follows: 1. Explicit reject route ("ip -6 route add unreachable 2001:db8::/64"): RTF_REJECT is set, enters reject path, skips fib_nh_common_init(). No behavior change. 2. Implicit loopback reject route ("ip -6 route add 2001:db8::/32 dev lo"): RTF_REJECT is not set, takes normal path, fib_nh_common_init() is called. ip6_route_info_create_nh() still promotes it to reject afterward. nhc_pcpu_rth_output is allocated but unused, which is harmless. 3. Standalone nexthop object ("ip -6 nexthop add id 100 dev lo"): RTF_REJECT is not set, takes normal path, fib_nh_common_init() is called. nhc_pcpu_rth_output is properly allocated, fixing the crash when IPv4 routes reference this nexthop.

References

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