VulnerabilityPublished 19 Jul 2026

CVE-2026-63968: Linux kernel · ipv6: fix possible infinite loop in fib6_select_path()

Source GCVE Database

Authoritative record:CVE-2026-63968· High 7.5

Not known to be exploited · CVSS 7.5 High · fixed in c87cd3cb309634bc8f50a54e2079424f219ac21f : patch Linux kernel soon.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.6% chance of exploitation in 30 days – higher than 51% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in c87cd3cb309634bc8f50a54e2079424f219ac21f, ab9a10969a907b472a0196d999c08ff7144172e3, 3948a7d92f7678e89e1776bb2d169afcad63b1ae +7

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 19 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 Oct 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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.

ghsa-c2hg-pgqh-6wp2

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected >=6.1.128 <6.1.176 >=6.6.75 <6.6.143 >=6.12.2 <6.12.93 >=6.11.11 <6.12	Fixed in c87cd3cb309634bc8f50a54e2079424f219ac21f ab9a10969a907b472a0196d999c08ff7144172e3 3948a7d92f7678e89e1776bb2d169afcad63b1ae 9c7da87c2dc860bb17ca1ece942495d28b1ce3b9 9b9d5bd6e3d4c9cecab5407604b690684b2532d2 6.12.93 6.12 6.6.143 6.1.176 0f7b73c3452635de83b8711b31abdda8e49aad7b
LinuxLinux	Affected =6.13	Fixed in–

AI-suggested

A fix for this vulnerability has been applied in the Linux kernel. Since this is a kernel-level issue, users should update to a kernel version that includes this patch once available.

Description

In the Linux kernel, the following vulnerability has been resolved: ipv6: fix possible infinite loop in fib6_select_path() Found while auditing the same pattern Sashiko reported in rt6_fill_node() [1]. Apply the same fix as commit f8d8ce1b515a ("ipv6: fix possible infinite loop in fib6_info_uses_dev()"). Writers holding tb6_lock can list_del_rcu(&first->fib6_siblings) without waiting for RCU readers; first->fib6_siblings.next then still points into the old ring and this softirq-side walker never reaches &first->fib6_siblings as its terminator. fib6_purge_rt() always WRITE_ONCE()s first->fib6_nsiblings to 0 before list_del_rcu(), so an inside-loop check is a reliable detach signal. [1] https://sashiko.dev/#/patchset/20260526020227.4857-1-jiayuan.chen%40linux.dev

Impact

The vulnerability could cause the kernel to enter an infinite loop during IPv6 route selection, potentially leading to a denial of service by consuming CPU resources indefinitely. There is no indication of code execution or privilege escalation from the provided data.

Summary

The Linux kernel IPv6 subsystem contained a flaw in fib6_select_path() where writers holding the tb6_lock could remove list entries without waiting for RCU readers, causing the fib6_siblings linked list to appear circular and resulting in a potential infinite loop during route selection. The fix applies a pattern previously used in a similar function (fib6_info_uses_dev()) to ensure that an inside-loop check reliably detects list detachment by WRITE_ONCE() updating a sibling count before removal. This prevents the softirq-side walker from looping indefinitely.

References

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