# CVE-2026-128239: GPAC through 26.07.0 NULL Pointer Dereference via MPEG-4 Form Handlers

Status: published. Published: 2026-11-13. Updated: 2026-11-13.

GPAC through 26.07.0 contains a NULL pointer dereference vulnerability in the MPEG-4 Form spatial-constraint handlers in src/compositor/mpeg4_form.c that lets attackers crash the process via unchecked group lookups. Attackers can supply a crafted XMT scene whose Form constraints reference a non-existent group, crashing tools like MP4Box during chapter import for denial of service.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/gpac/gpac/commit/bc416b997622e43de65afab3bae9b7d05d72f2b0

## Affected products and versions

- gpac / gpac (gpac/gpac): ≥ 0; ≤ 26.07.0 (affected, custom). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 6.8 (medium); CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N; source: CNA: VulnCheck

- CVSS 3.1: 5.5 (medium); CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H; source: CNA: VulnCheck

- CVSS 4.0: 6.8 (medium); CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X; source: NVD: disclosure@vulncheck.com

- CVSS 3.1: 5.5 (medium); CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H; source: NVD: disclosure@vulncheck.com

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-476

## Exploit evidence

- exploit: https://github.com/sigdevel/pocs/blob/main/res/gpac/MP4Box/221/221_ab_apply_compositor_mpeg4_form_c_627.xmt (CNA: VulnCheck)

## References

- https://github.com/gpac/gpac/issues/4029 (CNA: VulnCheck; issue-tracking)

- https://github.com/gpac/gpac/commit/bc416b997622e43de65afab3bae9b7d05d72f2b0 (CNA: VulnCheck; patch)

- https://github.com/gpac/gpac/blob/v26.07.0/src/compositor/mpeg4_form.c#L620-L621 (CNA: VulnCheck; technical-description)

- https://github.com/sigdevel/pocs/blob/main/res/gpac/MP4Box/221/221_ab_apply_compositor_mpeg4_form_c_627.xmt (CNA: VulnCheck; exploit)

- https://github.com/gpac/gpac (CNA: VulnCheck; product)

- https://www.vulncheck.com/advisories/gpac-through-26.07.0-null-pointer-dereference-via-mpeg-4-form-handlers (CNA: VulnCheck; third-party-advisory)

- https://github.com/gpac/gpac (disclosure@vulncheck.com)

- https://github.com/gpac/gpac/blob/v26.07.0/src/compositor/mpeg4_form.c#L620-L621 (disclosure@vulncheck.com)

- https://github.com/gpac/gpac/commit/bc416b997622e43de65afab3bae9b7d05d72f2b0 (disclosure@vulncheck.com)

- https://github.com/gpac/gpac/issues/4029 (disclosure@vulncheck.com)

- https://github.com/sigdevel/pocs/blob/main/res/gpac/MP4Box/221/221_ab_apply_compositor_mpeg4_form_c_627.xmt (disclosure@vulncheck.com)

- https://www.vulncheck.com/advisories/gpac-through-26.07.0-null-pointer-dereference-via-mpeg-4-form-handlers (disclosure@vulncheck.com)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-128239; retrieved 2026-11-13; source updated 2026-11-13

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-128239; retrieved 2026-11-13; source updated 2026-11-13

Revision: ed5af9a5086f7d861b38d670280c5c223993a463885e24c899c17965c582a16b

Canonical: https://y2.dev/cve/CVE-2026-128239

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

Collected public records only. Check source status for coverage and freshness.