MediumCVE-2026-68398

    Linux Kernel: Use After Free (CVE-2026-68398)

    Published Last modified Sources: SUSE, HKCERT, Ubuntu, Debian LTS, BSI, CVE.org, Msrc Update Guide

    Share

    What is affected, what to do

    In the Linux kernel, the following vulnerability has been resolved: ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF pppol2tp_recv() runs in the L2TP UDP-encap softirq RX path: l2tp_udp_encap_recv() -> l2tp_recv_common() -> pppol2tp_recv() -> ppp_input(&po->chan) It runs under rcu_read_lock() holding only an l2tp_session reference and takes NO reference on the internal PPP channel (struct channel, chan->ppp) that ppp_input() dereferences. The pppox socket is SOCK_RCU_FREE, so 'po' and the embedded ppp_channel are RCU-safe.

    An exploit is publicly available. The available sources name no fixed version. Check the vendor guidance in the references below.

    Conflicting version data — version display is hidden until the data is resolved.

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    4.7

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    4.7

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: SUSE, HKCERT, Ubuntu, Debian LTS, BSI, CVE.org, Msrc Update Guide

    0.2 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 14.2

    Show all metrics
    Severity
    Medium
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    47.55 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    PoC (publicly reported)
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    4.7 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    4.7
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.2 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    14.2
    Elevated — this CVE ranks above at least 10% of all CVEs scored today.
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CISA assessment (SSVC)
    Exploitation: none known · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 16 October 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-416

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    In the Linux kernel, the following vulnerability has been resolved: ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF pppol2tp_recv() runs in the L2TP UDP-encap softirq RX path: l2tp_udp_encap_recv() -> l2tp_recv_common() -> pppol2tp_recv() -> ppp_input(&po->chan) It runs under rcu_read_lock() holding only an l2tp_session reference and takes NO reference on the internal PPP channel (struct channel, chan->ppp) that ppp_input() dereferences. The pppox socket is SOCK_RCU_FREE, so 'po' and the embedded ppp_channel are RCU-safe. But the internal struct channel is a separate allocation that ppp_release_channel() frees with a plain kfree(): close(data socket) -> pppol2tp_release() -> pppox_unbind_sock() -> ppp_unregister_channel() -> ppp_release_channel() -> kfree(pch) For a channel that is bound (PPPIOCGCHAN) but not attached to a ppp unit (no PPPIOCCONNECT, pch->ppp == NULL) and not bridged, teardown skips both ppp_disconnect_channel()'s synchronize_net() and ppp_unbridge_channels()'s synchronize_rcu(), so the kfree() has no grace period. rcu_read_lock() in pppol2tp_recv() does not protect against a plain kfree(), so an in-flight ppp_input() on one CPU can dereference the channel just freed by close() on another CPU. The bug is reachable by an unprivileged user. Defer the channel free to an RCU callback via call_rcu() so the grace period fences any in-flight ppp_input(). The disconnect and unbridge teardown paths already fence with synchronize_net()/synchronize_rcu(); call_rcu() does the same here without stalling the close() path.

    Source: suse_csaf, HKCERT (CC BY 3.0 HK) · HKCERT rating: medium, Ubuntu Security Notices, Debian LTS Advisories, BSI WID Portal, BSI CSAF, cvelistv5, Microsoft Security Update Guide, NVD (NIST)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    LinuxLinux
    • 6.7 – < 6.12.101
    • 4.15 – < 5.15.216
    • 6.2 – < 6.6.148
    • 4.9.225 – < 4.10
    • 5.16 – < 6.1.183
    • 3.16.54 – < 3.17
    • 6.13 – < 6.18.42
    • 4.14.182 – < 4.15
    • —
    • 6.19 – < 7.1.6
    • 3.2.99 – < 3.3
    • 4.4.225 – < 4.5
    • 6.12.101
    • 5.15.216
    • 6.6.148
    • 4.10
    • 6.1.183
    • 3.17
    • 6.18.42
    • 4.15
    • 7.2
    • 7.1.6
    • 3.3
    • 4.5

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianlinuxbookworm
    Linuxubuntulinuxnoble
    Linuxubuntulinuxresolute
    Linuxdebianlinux-6.12bookworm
    Linuxubuntulinux-awsnoble
    Linuxubuntulinux-awsresolute
    Linuxubuntulinux-aws-7.0noble
    Linuxubuntulinux-aws-fipsnoble
    Linuxubuntulinux-azurenoble
    Linuxubuntulinux-azureresolute
    Linuxubuntulinux-azure-7.0noble
    Linuxubuntulinux-azure-fdenoble
    Linuxubuntulinux-azure-fderesolute
    Linuxubuntulinux-azure-fde-7.0noble
    Linuxubuntulinux-azure-fipsnoble
    Linuxubuntulinux-fipsnoble
    Linuxubuntulinux-gcpnoble
    Linuxubuntulinux-gcpresolute
    Linuxubuntulinux-gcp-7.0noble
    Linuxubuntulinux-gcp-fipsnoble
    Linuxubuntulinux-gkenoble
    Linuxubuntulinux-gkeresolute
    Linuxubuntulinux-gkeopnoble
    Linuxubuntulinux-hwe-7.0noble

    Weakness classes (CWE)

    • CWE-416Use After Free

      Variant

      The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

      Entry at MITRE CWE-416

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    PoC-in-GitHub (nomi-sec)CVE-2026-68398 (opens in a new tab)github.comPoC (publicly reported)reported, not verified

    References & sources

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedCISA ADP

      Weakness type: CWE-416

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Weakness type (CWE)added
      —
      CWE-416

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. Record modifiedLinux

      Show 14 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/06213c85d8c0994f786c093b8b2a517987943ca6
      Referenceadded
      —
      https://git.kernel.org/stable/c/110b765744b147c63882f5e9cb12931c5dc8d85f
      Referenceadded
      —
      https://git.kernel.org/stable/c/3ab32218d7182705dae5c86f13925f458072da2c
      Referenceadded
      —
      https://git.kernel.org/stable/c/4bb84e964ff0fe0a171c965362de72f9820dbce9
      Referenceadded
      —
      https://git.kernel.org/stable/c/4e47f1ac188ece11d6fdabe44166a2776cc5bd4e
      Referenceadded
      —
      https://git.kernel.org/stable/c/c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa
      Referenceadded
      —
      https://git.kernel.org/stable/c/ec4215683e47424c9c4762fd3c60f552a3119142
      Referenceremoved
      https://git.kernel.org/stable/c/06213c85d8c0994f786c093b8b2a517987943ca6
      —
      Referenceremoved
      https://git.kernel.org/stable/c/110b765744b147c63882f5e9cb12931c5dc8d85f
      —
      Referenceremoved
      https://git.kernel.org/stable/c/3ab32218d7182705dae5c86f13925f458072da2c
      —
      Referenceremoved
      https://git.kernel.org/stable/c/4bb84e964ff0fe0a171c965362de72f9820dbce9
      —
      Referenceremoved
      https://git.kernel.org/stable/c/4e47f1ac188ece11d6fdabe44166a2776cc5bd4e
      —
      Referenceremoved
      https://git.kernel.org/stable/c/c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa
      —
      Referenceremoved
      https://git.kernel.org/stable/c/ec4215683e47424c9c4762fd3c60f552a3119142
      —

      Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

    3. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: no

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2026-68398","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:48:09.975001Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    4. Record modifiedLinux

      Show 3 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/110b765744b147c63882f5e9cb12931c5dc8d85f
      Referenceadded
      —
      https://git.kernel.org/stable/c/4e47f1ac188ece11d6fdabe44166a2776cc5bd4e
      Affected versions (publisher)changed
      Linux, Linux
      Linux, Linux

      Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

    5. Record modifiedLinux

      1 individual change: Affected versions (publisher)

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)changed
      Linux, Linux
      Linux, Linux

      Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

    Show one older change

    1. ReceivedLinux

      Description added or changed

      Show 7 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      Linux, Linux
      Descriptionadded
      —
      In the Linux kernel, the following vulnerability has been resolved: ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF pppol2tp_recv() runs in the L2TP UDP-encap softirq RX path: l2tp_udp_encap_recv() -> l2tp_recv_common() -> pppol2tp_recv() -> ppp_input(&po->chan) It runs under rcu_read_lock() holding only an l2tp_session reference and takes NO reference on the internal PPP channel (struct channel, chan->ppp) that ppp_input() dereferences. The pppox socket is SOCK_RCU_FREE, so 'po' and the embedded ppp_channel are RCU-safe. But the internal struct channel is a separate allocation that ppp_release_channel() frees with a plain kfree(): close(data socket) -> pppol2tp_release() -> pppox_unbind_sock() -> ppp_unregister_channel() -> ppp_release_channel() -> kfree(pch) For a channel that is bound (PPPIOCGCHAN) but not attached to a ppp unit (no PPPIOCCONNECT, pch->ppp == NULL) and not bridged, teardown skips both ppp_disconnect_channel()'s synchronize_net() and ppp_unbridge_channels()'s synchronize_rcu(), so the kfree() has no grace period. rcu_read_lock() in pppol2tp_recv() does not protect against a plain kfree(), so an in-flight ppp_input() on one CPU can dereference the channel just freed by close() on another CPU. The bug is reachable by an unprivileged user. Defer the channel free to an RCU callback via call_rcu() so the grace period fences any in-flight ppp_input(). The disconnect and unbridge teardown paths already fence with synchronize_net()/synchronize_rcu(); call_rcu() does the same here without stalling the close() path.
      Referenceadded
      —
      https://git.kernel.org/stable/c/06213c85d8c0994f786c093b8b2a517987943ca6
      Referenceadded
      —
      https://git.kernel.org/stable/c/3ab32218d7182705dae5c86f13925f458072da2c
      Referenceadded
      —
      https://git.kernel.org/stable/c/4bb84e964ff0fe0a171c965362de72f9820dbce9
      Referenceadded
      —
      https://git.kernel.org/stable/c/c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa
      Referenceadded
      —
      https://git.kernel.org/stable/c/ec4215683e47424c9c4762fd3c60f552a3119142

      Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

    Embed badge

    Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.

    Badge preview for CVE-2026-68398
    <a href="https://intel.neosec.eu/en/cve/CVE-2026-68398"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-68398.svg?lang=en" alt="CVE-2026-68398 – NEOSEC Intel" height="20"></a>