# CVE-2026-109445: PLANET GS-5220-8P2T2S Stack Buffer Overflow via webstax_auth Cookie

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

PLANET GS-5220-8P2T2S (hardware version 3.0) firmware versions before 3.2412b261008 contains a stack-based buffer overflow vulnerability that allows unauthenticated attackers to corrupt stack memory by submitting an oversized webstax_auth HTTP Cookie value that is copied into a fixed-size stack buffer without length validation. Attackers can send a crafted unauthenticated HTTP request with an oversized cookie to overwrite the saved return address and corrupt stack memory, leading to memory corruption and potential denial of service on the device.

## 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://www.planet.com.tw/en/support/security-advisory/12

## Affected products and versions

- PLANET Technology Corp. / PLANET GS-5220-8P2T2S: ≥ 0; < 3.2412b261008 (affected, custom). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 9.3 (critical); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N; source: CNA: VulnCheck

- CVSS 3.1: 9.8 (critical); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H; source: CNA: VulnCheck

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-121

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://www.planet.com.tw/en/support/security-advisory/12 (CNA: VulnCheck; vendor-advisory, patch)

- https://www.vulncheck.com/advisories/planet-gs-5220-8p2t2s-stack-buffer-overflow-via-webstax-auth-cookie (CNA: VulnCheck; third-party-advisory)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-109445; retrieved 2026-11-13; source updated 2026-11-13

Revision: 8716f9c3a084e683c16b5cb6bdc5a9b7f9237ec69eaa32431d6728e7154615fa

Canonical: https://y2.dev/cve/CVE-2026-109445

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