CVE-2026-64538

ipv6: Fix null-ptr-deref in fib6_nh_mtu_change().

Published Jul 27, 2026 CVSS 3.1 · 7.0 High EPSS < 1% KEV · Not listed

Description

In the Linux kernel, the following vulnerability has been resolved:

ipv6: Fix null-ptr-deref in fib6_nh_mtu_change().

fib6_nh_mtu_change() re-fetches idev via __in6_dev_get(arg->dev) and
dereferences idev->cnf.mtu6 without a NULL check. addrconf_ifdown()
clears dev->ip6_ptr with RCU_INIT_POINTER() after rt6_disable_ip() has
released tb6_lock, so the RA-driven MTU walk can observe a NULL idev and
oops. The caller rt6_mtu_change_route() guards its own __in6_dev_get(),
but this re-fetch is unguarded; nexthop-backed routes survive
addrconf_ifdown()'s flush, so the walk still reaches it after ip6_ptr is
nulled.

Return 0 when idev is NULL, matching rt6_mtu_change_route() and the
fib6_mtu() fix in commit 5ad509c1fdad ("ipv6: Fix null-ptr-deref in
fib6_mtu().").

Oops: general protection fault, ... KASAN: null-ptr-deref in range
[0x00000000000002a8-0x00000000000002af]
RIP: 0010:fib6_nh_mtu_change+0x203/0x990
rt6_mtu_change_route+0x141/0x1d0
__fib6_clean_all+0xd0/0x160
rt6_mtu_change+0xb4/0x100
ndisc_router_discovery+0x24b5/0x2cb0
icmpv6_rcv+0x12e9/0x1710
ipv6_rcv+0x39b/0x410

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`c0b220cf7d80eb8a36ae9f12cae6df4577a6814e`	affected	< d08d019f2f43a6f9a71e81868bbc326b3afaf37b
`c0b220cf7d80eb8a36ae9f12cae6df4577a6814e`	affected	< 1451deca9896957159f0666520a792c1b861af4f
`c0b220cf7d80eb8a36ae9f12cae6df4577a6814e`	affected	< b2c70dd3326809429b709a9c7e9220d29923051a
`c0b220cf7d80eb8a36ae9f12cae6df4577a6814e`	affected	< 302d57ed7872838b40e56a868fb4c7da7da606e9
`c0b220cf7d80eb8a36ae9f12cae6df4577a6814e`	affected	< 80600b5d0f3ecb9324120dc95b5e915130f516c5
`c0b220cf7d80eb8a36ae9f12cae6df4577a6814e`	affected	< b0d0eb13a0441a8ebf4f227843deaf494f1e2c33
`c0b220cf7d80eb8a36ae9f12cae6df4577a6814e`	affected	< 6428634f7a0b7878144b4925c37856bef3224967
`c0b220cf7d80eb8a36ae9f12cae6df4577a6814e`	affected	< 46c3b8191aad3d032776bf3bebf03efdf5f4b905

Linux

affected

Version	Status	Constraints
`5.3`	affected	—
`0`	unaffected	< 5.3
`5.10.261`	unaffected	≤ 5.10.*
`5.15.212`	unaffected	≤ 5.15.*
`6.1.178`	unaffected	≤ 6.1.*
`6.6.145`	unaffected	≤ 6.6.*
`6.12.97`	unaffected	≤ 6.12.*
`6.18.40`	unaffected	≤ 6.18.*
`7.1.5`	unaffected	≤ 7.1.*
`7.2`	unaffected	≤ *

No data.

Vendor Product Versions

Linux

Linux Kernel

Version	Status	Scheme	Platform
`[c0b220cf7d80eb8a36ae9f12cae6df4577a6814e,d08d019f2f43a6f9a71e81868bbc326b3afaf37b)`	affected	code_commit	—
`[c0b220cf7d80eb8a36ae9f12cae6df4577a6814e,1451deca9896957159f0666520a792c1b861af4f)`	affected	code_commit	—
`[c0b220cf7d80eb8a36ae9f12cae6df4577a6814e,b2c70dd3326809429b709a9c7e9220d29923051a)`	affected	code_commit	—
`[c0b220cf7d80eb8a36ae9f12cae6df4577a6814e,302d57ed7872838b40e56a868fb4c7da7da606e9)`	affected	code_commit	—
`[c0b220cf7d80eb8a36ae9f12cae6df4577a6814e,80600b5d0f3ecb9324120dc95b5e915130f516c5)`	affected	code_commit	—
`[c0b220cf7d80eb8a36ae9f12cae6df4577a6814e,b0d0eb13a0441a8ebf4f227843deaf494f1e2c33)`	affected	code_commit	—
`[c0b220cf7d80eb8a36ae9f12cae6df4577a6814e,6428634f7a0b7878144b4925c37856bef3224967)`	affected	code_commit	—
`[c0b220cf7d80eb8a36ae9f12cae6df4577a6814e,46c3b8191aad3d032776bf3bebf03efdf5f4b905)`	affected	code_commit	—

Linux

Linux Kernel

Version	Status	Scheme	Platform
`5.3`	affected	semver	—
`[0,5.3)`	unaffected	semver	—
`[5.10.261,5.11.0)`	unaffected	semver	—
`[5.15.212,5.16.0)`	unaffected	semver	—
`[6.1.178,6.2.0)`	unaffected	semver	—
`[6.6.145,6.7.0)`	unaffected	semver	—
`[6.12.97,6.13.0)`	unaffected	semver	—
`[6.18.40,6.19.0)`	unaffected	semver	—
`[7.1.5,7.2.0)`	unaffected	semver	—
`[7.2-rc1,*]`	unaffected	generic	—

Remediation

No solution or workaround provided in the CVE record

Tracking

Advisories

Source	ID	Title
Debian DLA	DLA-4717-1	linux security update
Debian DLA	DLA-4720-1	linux security update
Debian DLA	DLA-4723-1	linux-6.1 security update
Debian DLA	DLA-4724-1	linux-6.12 new package
Debian DSA	DSA-6405-1	linux security update
Ubuntu USN	USN-8876-1	Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN	USN-8875-1	Linux kernel vulnerabilities
Ubuntu USN	USN-8877-1	Linux kernel (GCP) vulnerabilities
Ubuntu USN	USN-8878-1	Linux kernel (GCP) vulnerabilities
Ubuntu USN	USN-8879-1	Linux kernel (Oracle) vulnerabilities
Ubuntu USN	USN-8887-1	Linux kernel vulnerabilities
Ubuntu USN	USN-8888-1	Linux kernel (Azure) vulnerabilities
Ubuntu USN	USN-8889-1	Linux kernel (OEM) vulnerabilities
Ubuntu USN	USN-8887-2	Linux kernel (AWS) vulnerabilities
Ubuntu USN	USN-8888-2	Linux kernel (Azure) vulnerabilities
Ubuntu USN	USN-8875-2	Linux kernel (NVIDIA) vulnerabilities
Ubuntu USN	USN-8887-3	Linux kernel vulnerabilities
Ubuntu USN	USN-8917-1	Linux kernel vulnerabilities
Ubuntu USN	USN-8918-1	Linux kernel (Azure) vulnerabilities
Ubuntu USN	USN-9003-1	Linux kernel (NVIDIA) vulnerabilities
Ubuntu USN	USN-9024-1	Linux kernel vulnerabilities
Ubuntu USN	USN-9025-1	Linux kernel vulnerabilities
Ubuntu USN	USN-9026-1	Linux kernel (Azure) vulnerabilities
Ubuntu USN	USN-9029-1	Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN	USN-9040-1	Linux kernel (Low Latency NVIDIA) vulnerabilities
Ubuntu USN	USN-9043-1	Linux kernel (NVIDIA) vulnerabilities
Ubuntu USN	USN-9066-1	Linux kernel (HWE) vulnerabilities
Ubuntu USN	USN-9091-1	Linux kernel (NVIDIA Tegra) vulnerabilities

Metrics

No CVSS v4.0

Attack Vector Local

Attack Complexity High

Privileges Required Low

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.200% probability within 30 days)

Exploitation none

Automatable no

Technical Impact partial

References

Link	Providers
https://cert-portal.siemens.com/productcert/html/ssa-019113.html
https://cert-portal.siemens.com/productcert/html/ssa-457936.html
https://git.kernel.org/stable/c/1451deca9896957159f0666520a792c1b861af4f
https://git.kernel.org/stable/c/302d57ed7872838b40e56a868fb4c7da7da606e9
https://git.kernel.org/stable/c/46c3b8191aad3d032776bf3bebf03efdf5f4b905
https://git.kernel.org/stable/c/6428634f7a0b7878144b4925c37856bef3224967
https://git.kernel.org/stable/c/80600b5d0f3ecb9324120dc95b5e915130f516c5
https://git.kernel.org/stable/c/b0d0eb13a0441a8ebf4f227843deaf494f1e2c33
https://git.kernel.org/stable/c/b2c70dd3326809429b709a9c7e9220d29923051a
https://git.kernel.org/stable/c/d08d019f2f43a6f9a71e81868bbc326b3afaf37b
https://lore.kernel.org/linux-cve-announce/2026072735-CVE-2026-64538-1a88@gregkh/T
https://nvd.nist.gov/vuln/detail/CVE-2026-64538
https://www.cve.org/CVERecord?id=CVE-2026-64538

History

Nov 7, 2026 7:30 AM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Oct 15, 2026 2:30 AM Added references View changes

Type	Values Removed	Values Added
References		https://cert-portal.siemens.com/productcert/html/ssa-457936.html

Sep 8, 2026 9:30 AM Added references View changes

Type	Values Removed	Values Added
References		https://cert-portal.siemens.com/productcert/html/ssa-019113.html

Jul 29, 2026 12:15 AM Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
References		https://lore.kernel.org/linux-cve-announce/2026072735-CVE-2026-64538-1a88@gregkh/T https://nvd.nist.gov/vuln/detail/CVE-2026-64538 https://www.cve.org/CVERecord?id=CVE-2026-64538
Metrics	threat_severity `None`	cvssV3_1 `{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}` threat_severity `Moderate`

Jul 28, 2026 4:15 PM Weaknesses updated View changes

Type	Values Removed	Values Added
Weaknesses		CWE-476

Jul 27, 2026 8:30 PM Description updated. Title updated. First appearance in the feed. Affected versions updated. Affected vendors updated. Added references View changes

Type	Values Removed	Values Added
Description		In the Linux kernel, the following vulnerability has been resolved: ipv6: Fix null-ptr-deref in fib6_nh_mtu_change(). fib6_nh_mtu_change() re-fetches idev via __in6_dev_get(arg->dev) and dereferences idev->cnf.mtu6 without a NULL check. addrconf_ifdown() clears dev->ip6_ptr with RCU_INIT_POINTER() after rt6_disable_ip() has released tb6_lock, so the RA-driven MTU walk can observe a NULL idev and oops. The caller rt6_mtu_change_route() guards its own __in6_dev_get(), but this re-fetch is unguarded; nexthop-backed routes survive addrconf_ifdown()'s flush, so the walk still reaches it after ip6_ptr is nulled. Return 0 when idev is NULL, matching rt6_mtu_change_route() and the fib6_mtu() fix in commit 5ad509c1fdad ("ipv6: Fix null-ptr-deref in fib6_mtu()."). Oops: general protection fault, ... KASAN: null-ptr-deref in range [0x00000000000002a8-0x00000000000002af] RIP: 0010:fib6_nh_mtu_change+0x203/0x990 rt6_mtu_change_route+0x141/0x1d0 __fib6_clean_all+0xd0/0x160 rt6_mtu_change+0xb4/0x100 ndisc_router_discovery+0x24b5/0x2cb0 icmpv6_rcv+0x12e9/0x1710 ipv6_rcv+0x39b/0x410
Title		ipv6: Fix null-ptr-deref in fib6_nh_mtu_change().
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/1451deca9896957159f0666520a792c1b861af4f https://git.kernel.org/stable/c/302d57ed7872838b40e56a868fb4c7da7da606e9 https://git.kernel.org/stable/c/46c3b8191aad3d032776bf3bebf03efdf5f4b905 https://git.kernel.org/stable/c/6428634f7a0b7878144b4925c37856bef3224967 https://git.kernel.org/stable/c/80600b5d0f3ecb9324120dc95b5e915130f516c5 https://git.kernel.org/stable/c/b0d0eb13a0441a8ebf4f227843deaf494f1e2c33 https://git.kernel.org/stable/c/b2c70dd3326809429b709a9c7e9220d29923051a https://git.kernel.org/stable/c/d08d019f2f43a6f9a71e81868bbc326b3afaf37b