CVE-2026-63918: Software Security Vulnerability Vulnerability

HIGH
Advisory Identifier: GHSA-9qwr-gw6x-fmgj
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CVSS 7.8
Published
Advisory Summary

CVE-2026-63918 is a HIGH (CVSS 7.8) security vulnerability vulnerability (General Security Weakness) affecting Software libraries in the Maven ecosystem. Remediation is available in the latest vendor maintenance releases.

CVE-2026-63918 at a Glance

CVE Identifier CVE-2026-63918
GHSA Identifier GHSA-9qwr-gw6x-fmgj
Severity HIGH
CVSS v3.1 Base Score 7.8
CWE Classification General Security Weakness
Affected Product Software
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 7.8

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H).

Attack Vector Local (AV:L)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2026-63918

To remediate this vulnerability, upgrade all affected Software dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2026-63918, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree

Analyze the terminal output to locate any version of Software in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The mvn dependency:tree command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under General Security Weakness. In Software, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

In the Linux kernel, the following vulnerability has been resolved: l2tp: use refcount_inc_not_zero in l2tp_session_get_by_ifname A reader in l2tp_session_get_by_ifname() can return a pointer to a session whose refcount has reached zero. The getter takes its reference with plain refcount_inc(), but every other session getter in the same file (l2tp_v2_session_get, l2tp_v3_session_get, and the corresponding _get_next variants) uses refcount_inc_not_zero() because the IDR/RCU lookup can race with refcount_dec_and_test() -> l2tp_session_free() -> kfree_rcu(). The ifname getter is the only outlier; the inconsistency was raised on-list after 979c017803c4 ("l2tp: use list_del_rcu in l2tp_session_unhash"). A reader inside rcu_read_lock_bh() that matches session->ifname can be preempted between the strcmp() and the refcount_inc(). If the last reference drops on another CPU in that window, the reader's refcount_inc() runs on a counter that has reached zero. refcount_t catches the addition-on-zero, prints "refcount_t: addition on 0; use-after-free", saturates the counter, and returns the saturated pointer to the caller. Session memory is held live by the in-flight RCU read section, but the kfree_rcu() callback queued from l2tp_session_free() will free it once the grace period closes; a caller that dereferences the returned session past that point hits a slab-use-after-free. On PREEMPT_RT local_bh_disable() is a per-CPU sleeping lock and the preemption window is real; on stock PREEMPT kernels local_bh_disable() is a preempt_count increment that closes the cross-CPU race in practice (see below). Use refcount_inc_not_zero() and continue the list walk on failure, matching the other session getters in the file. The ifname getter is the only session getter in net/l2tp/ that still uses the bare refcount_inc() pattern; this change restores file-internal consistency. The success path is unchanged.

References

NVD — CVE-2026-63918 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-63918
git.kernel.org/stable/c/05f95729ca... WEB
https://git.kernel.org/stable/c/05f95729ca844704d15e49ce14868af4b403b32b
git.kernel.org/stable/c/782d60a659... WEB
https://git.kernel.org/stable/c/782d60a6596aee9b29c2eecfa70033899278bf65
git.kernel.org/stable/c/947013fd7c... WEB
https://git.kernel.org/stable/c/947013fd7c8c35dd5856557b215840098a3f67f8
git.kernel.org/stable/c/ee80455fef... WEB
https://git.kernel.org/stable/c/ee80455feffb9cb62b5b58715cabeff495e666b2

Frequently Asked Questions

What is CVE-2026-63918?
CVE-2026-63918 is a security vulnerability in Software classified as a security vulnerability vulnerability under General Security Weakness.
Which Software versions are affected?
Affected versions include releases prior to current release patches.
What version fixes CVE-2026-63918?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
What is the CVSS score of CVE-2026-63918?
CVE-2026-63918 has a CVSS v3.1 base score of 7.8 (HIGH) with vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2026-63918?
CVE-2026-63918 is classified under General Security Weakness.
How can I check Maven dependencies for CVE-2026-63918?
Run the dependency tree command: 'mvn dependency:tree'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-9qwr-gw6x-fmgj",
  "modified" : "2026-07-20T15:31:51Z",
  "published" : "2026-07-19T18:31:46Z",
  "aliases" : [ "CVE-2026-63918" ],
  "details" : "In the Linux kernel, the following vulnerability has been resolved:\n\nl2tp: use refcount_inc_not_zero in l2tp_session_get_by_ifname\n\nA reader in l2tp_session_get_by_ifname() can return a pointer to a\nsession whose refcount has reached zero. The getter takes its\nreference with plain refcount_inc(), but every other session getter\nin the same file (l2tp_v2_session_get, l2tp_v3_session_get, and the\ncorresponding _get_next variants) uses refcount_inc_not_zero()\nbecause the IDR/RCU lookup can race with refcount_dec_and_test() ->\nl2tp_session_free() -> kfree_rcu(). The ifname getter is the only\noutlier; the inconsistency was raised on-list after 979c017803c4\n(\"l2tp: use list_del_rcu in l2tp_session_unhash\").\n\nA reader inside rcu_read_lock_bh() that matches session->ifname can\nbe preempted between the strcmp() and the refcount_inc(). If the\nlast reference drops on another CPU in that window, the reader's\nrefcount_inc() runs on a counter that has reached zero. refcount_t\ncatches the addition-on-zero, prints \"refcount_t: addition on 0;\nuse-after-free\", saturates the counter, and returns the saturated\npointer to the caller. Session memory is held live by the in-flight\nRCU read section, but the kfree_rcu() callback queued from\nl2tp_session_free() will free it once the grace period closes; a\ncaller that dereferences the returned session past that point hits\na slab-use-after-free. On PREEMPT_RT local_bh_disable() is a per-CPU\nsleeping lock and the preemption window is real; on stock PREEMPT\nkernels local_bh_disable() is a preempt_count increment that closes\nthe cross-CPU race in practice (see below).\n\nUse refcount_inc_not_zero() and continue the list walk on failure,\nmatching the other session getters in the file. The ifname getter\nis the only session getter in net/l2tp/ that still uses the bare\nrefcount_inc() pattern; this change restores file-internal\nconsistency. The success path is unchanged.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-63918"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/05f95729ca844704d15e49ce14868af4b403b32b"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/782d60a6596aee9b29c2eecfa70033899278bf65"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/947013fd7c8c35dd5856557b215840098a3f67f8"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/ee80455feffb9cb62b5b58715cabeff495e666b2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ ],
    "severity" : "HIGH",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-07-19T16:17:09Z"
  }
}