Zyxel VMG8825-T50K firmware: Classic Buffer Overflow (CVE-2025-7673)
Published Sources: CVE.org
- Actively exploited
- Source: VulnCheck KEV (opens in a new tab) How we classify
What is affected, what to do
A buffer overflow vulnerability in the URL parser of the zhttpd web server in Zyxel VMG8825-T50K firmware versions prior to V5.50(ABOM.5)C0 could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions and potentially execute arbitrary code by sending a specially crafted HTTP request.
The vulnerability is being actively exploited; treat it as a priority. Update Zyxel VMG8825-T50K firmware to version V5.50(ABOM.5)C0.
- Affected
- Zyxel VMG8825-T50K firmware
lt *..V5.50(ABOM.5)C0
- Zyxel VMG8825-T50K firmware
- Fixed in
- Zyxel VMG8825-T50K firmware
V5.50(ABOM.5)C0
- Zyxel VMG8825-T50K firmware
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Metrics
9.8
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
9.8
CVSS v3
Severity Critical on the scale from 0 to 10.
Source: CVE.org
0.7 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 51.5
Show all metrics
- Severity
- Critical
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- 79.99 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- actively exploitedSource: VulnCheck KEV (opens in a new tab) How we classify
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- 9.8 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- 9.8
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- 0.7 %
- 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- 51.5
- High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
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 · automatable · Technical impact: total
- Source: CISA Vulnrichment, as of 19 July 2025
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-120
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- Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
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- Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
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
A buffer overflow vulnerability in the URL parser of the zhttpd web server in Zyxel VMG8825-T50K firmware versions prior to V5.50(ABOM.5)C0 could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions and potentially execute arbitrary code by sending a specially crafted HTTP request.
Source: cvelistv5, NVD (NIST), CVE.org (MITRE)
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| Zyxel | VMG8825-T50K firmware |
|
|
Vendors and products
- Zyxel Zyxel EMG3525-T50B FIRMWARE 5.50(ABPM.9.8)C0
- Zyxel Zyxel EMG5523-T50B FIRMWARE 5.50(ABPM.9.8)C0
- Zyxel Emg5723-t50k Firmware
- Zyxel Emg6726-b10a Firmware
- Zyxel Zyxel EX3510-B0 firmware
- Zyxel Ex5510-b0 Firmware
- Zyxel Vmg1312-t20b Firmware
- Zyxel Zyxel VMG3625-T50B firmware
- Zyxel Vmg3927-b50a Firmware
- Zyxel Vmg3927-b50b Firmware
- Zyxel Vmg3927-b60a Firmware
- Zyxel Vmg3927-t50k Firmware
Affected operating systems
| Other | zyxel | emg3525-t50b_firmware | — |
| Other | zyxel | emg5523-t50b_firmware | — |
| Other | zyxel | emg5723-t50k_firmware | — |
| Other | zyxel | emg6726-b10a_firmware | — |
| Other | zyxel | ex3510-b0_firmware | — |
| Other | zyxel | ex5510-b0_firmware | — |
| Other | zyxel | vmg1312-t20b_firmware | — |
| Other | zyxel | vmg3625-t50b_firmware | — |
| Other | zyxel | vmg3925-b10b_firmware | — |
| Other | zyxel | vmg3925-b10c_firmware | — |
| Other | zyxel | vmg3927-b50a_firmware | — |
| Other | zyxel | vmg3927-b50b_firmware | — |
| Other | zyxel | vmg3927-b60a_firmware | — |
| Other | zyxel | vmg3927-t50k_firmware | — |
| Other | zyxel | vmg4005-b50b_firmware | — |
| Other | zyxel | vmg4927-b50a_firmware | — |
| Other | zyxel | vmg8623-t50b_firmware | — |
| Other | zyxel | vmg8825-b50a_firmware | — |
| Other | zyxel | vmg8825-b60a_firmware | — |
| Other | zyxel | vmg8825-bx0b_firmware | — |
| Other | zyxel | vmg8825-t50k_firmware | — |
| Other | zyxel | vmg8924-b10d_firmware | — |
| Other | zyxel | xmg3927-b50a_firmware | — |
| Other | zyxel | xmg8825-b50a_firmware | — |
Weakness classes (CWE)
CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
Base
The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer.
Entry at MITRE CWE-120
References & sources
- zyxel.comservice-provider/global/en/zyxel-security-advisory-remote-code-…Vendor advisory, Vendor advisory
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<a href="https://intel.neosec.eu/en/cve/CVE-2025-7673"><img src="https://intel.neosec.eu/badge/cve/CVE-2025-7673.svg?lang=en" alt="CVE-2025-7673 – NEOSEC Intel" height="20"></a>