CVE-2026-63939: Software Security Vulnerability Vulnerability

CRITICAL
Advisory Identifier: GHSA-94xr-m4g8-q6cc
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CVSS 9.3
CWE-122
Published
Advisory Summary

CVE-2026-63939 is a CRITICAL (CVSS 9.3) security vulnerability vulnerability (CWE-122: Heap-based Buffer Overflow) affecting Software libraries in the Maven ecosystem. The weakness occurs when a heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().. Remediation is available in the latest vendor maintenance releases.

CVE-2026-63939 at a Glance

CVE Identifier CVE-2026-63939
GHSA Identifier GHSA-94xr-m4g8-q6cc
Severity CRITICAL
CVSS v3.1 Base Score 9.3
CWE Classification CWE-122: Heap-based Buffer Overflow
Affected Product Software
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 9.3

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

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

How to Fix CVE-2026-63939

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-2026-63939, 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 CWE-122: Heap-based Buffer Overflow, where a heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc(). 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: KVM: SEV: Compute the correct max length of the in-GHCB scratch area When setting the length of the GHCB scratch area, and the area is in the GHCB shared buffer, set the effective length of the scratch area to the max possible size given the start of the guest-provided pointer, and the end of the shared buffer. The code was "fine" when first introduced, as KVM doesn't consult the length of the buffer when emulating MMIO, because the passed in @len always specifies the *max* size required. But for PSC requests, the incoming @len is just the minimum length (to process the header), and KVM needs to know the full size of the scratch area to avoid buffer overflows (spoiler alert). Opportunistically rename @len => @min_len to better reflect its role.

References

NVD — CVE-2026-63939 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-63939
git.kernel.org/stable/c/5867d7e202... WEB
https://git.kernel.org/stable/c/5867d7e202e09f037cefe77f7af4413c7c0fa088
git.kernel.org/stable/c/6644565527... WEB
https://git.kernel.org/stable/c/6644565527c4c5f507088b1c9ddf72de47790b68
git.kernel.org/stable/c/6ca9400d36... WEB
https://git.kernel.org/stable/c/6ca9400d36005ffdca25f80186bea781c7e1dc4c
git.kernel.org/stable/c/9f0a9e780f... WEB
https://git.kernel.org/stable/c/9f0a9e780f02c02d025a190f1885e1d1d73b87bd

Frequently Asked Questions

What is CVE-2026-63939?
CVE-2026-63939 is a security vulnerability in Software classified as a security vulnerability vulnerability under CWE-122: Heap-based Buffer Overflow.
Which Software versions are affected?
Affected versions include releases prior to current release patches.
What version fixes CVE-2026-63939?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
What is the CVSS score of CVE-2026-63939?
CVE-2026-63939 has a CVSS v3.1 base score of 9.3 (CRITICAL) with vector string CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H.
What CWE is associated with CVE-2026-63939?
CVE-2026-63939 is classified under CWE-122: Heap-based Buffer Overflow (A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().).
How can I check Maven dependencies for CVE-2026-63939?
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-94xr-m4g8-q6cc",
  "modified" : "2026-07-20T15:31:52Z",
  "published" : "2026-07-19T18:31:46Z",
  "aliases" : [ "CVE-2026-63939" ],
  "details" : "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SEV: Compute the correct max length of the in-GHCB scratch area\n\nWhen setting the length of the GHCB scratch area, and the area is in the\nGHCB shared buffer, set the effective length of the scratch area to the max\npossible size given the start of the guest-provided pointer, and the end of\nthe shared buffer.\n\nThe code was \"fine\" when first introduced, as KVM doesn't consult the\nlength of the buffer when emulating MMIO, because the passed in @len always\nspecifies the *max* size required.  But for PSC requests, the incoming @len\nis just the minimum length (to process the header), and KVM needs to know\nthe full size of the scratch area to avoid buffer overflows (spoiler alert).\n\nOpportunistically rename @len => @min_len to better reflect its role.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H"
  } ],
  "affected" : [ ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-63939"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/5867d7e202e09f037cefe77f7af4413c7c0fa088"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/6644565527c4c5f507088b1c9ddf72de47790b68"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/6ca9400d36005ffdca25f80186bea781c7e1dc4c"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/9f0a9e780f02c02d025a190f1885e1d1d73b87bd"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-122" ],
    "severity" : "CRITICAL",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-07-19T16:17:12Z"
  }
}