Cyber Resilience

CVE-2025-6599

DoS in Zyxel Ex3300-T0 Firmware ≤ 5.50\(abvy.6.3\)c0

Published
18 November 2025
Modified
16 December 2025
Patch / advisory
CVSS Score v3.1 5.3
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
EPSS Score 0.0031 23th percentile
Risk Priority 35 floored blend · peak EPSS

Summary

CVE-2025-6599 is a medium-severity Uncontrolled Resource Consumption (CWE-400) vulnerability in Zyxel Ex3300-T0 Firmware. Its CVSS base score is 5.3 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Application Exhaustion Flood (T1499.003); ranked at the 23th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SC-5 (Denial-of-service Protection) and SC-7 (Boundary Protection) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

An uncontrolled resource consumption vulnerability in the web server of Zyxel DX3301-T0 firmware version 5.50(ABVY.6.3)C0 and earlier could allow an attacker to perform Slowloris‑style denial‑of‑service (DoS) attacks. Such attacks may temporarily block legitimate HTTP requests and partially disrupt access to…

more

the web management interface, while other networking services remain unaffected.

CWE(s)

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1499.003 Application Exhaustion Flood Impact
Adversaries may target resource intensive features of applications to cause a denial of service (DoS), denying availability to those applications.
Why these techniques?

Directly enables application-layer resource exhaustion DoS via Slowloris-style HTTP connection holding (CWE-400) against the web server.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2025-8693Same product: Zyxel Ax7501-B0
CVE-2025-11847Same product: Zyxel Ax7501-B1
CVE-2025-11846Same product: Zyxel Ax7501-B1
CVE-2025-11845Same product: Zyxel Ax7501-B1
CVE-2025-13943Same product: Zyxel Ax7501-B1
CVE-2025-11848Same product: Zyxel Ax7501-B1
CVE-2024-8748Same product: Zyxel Ax7501-B0
CVE-2024-5412Same product: Zyxel Ax7501-B0
CVE-2024-38266Same product: Zyxel Ax7501-B0
CVE-2024-38268Same product: Zyxel Ax7501-B1

Affected Assets

zyxel
lte3301-plus firmware
≤ 1.00\(abqu.7\)c0
zyxel
nr5103 firmware
≤ 4.19\(abyc.8\)c0
zyxel
nr5103e firmware
≤ 1.00\(acdj.1\)c0
zyxel
nr5309 firmware
≤ 1.00\(ackp.1\)b3
zyxel
nr7302 firmware
≤ 5.00\(acha.5\)c0
zyxel
nr7303 firmware
≤ 1.00\(acei.1\)c0
zyxel
nebula fwa505 firmware
≤ 1.19\(acko.0\)c0
zyxel
nebula fwa510 firmware
≤ 1.20\(acgd.1\)c0
zyxel
nebula fwa515 firmware
≤ 1.50\(acpz.0\)c0
zyxel
nebula fwa710 firmware
≤ 1.20\(acgc.0\)c0
+56 more product configuration(s) — see NVD for full list

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • SC-5 Denial-of-service Protection
  • SC-7 Boundary Protection
Detect
Catch it (NIST detect / respond)
  • SI-4 System Monitoring
Harden
Shrink the surface (DISA STIG)

Validate
Prove the fix (OWASP ASVS)

Mitigating Controls (NIST 800-53 r5) AI

prevent

Directly requires protection against or limiting of denial-of-service attacks such as Slowloris-style resource exhaustion on the web server.

prevent

Boundary protection mechanisms can enforce connection rate limits, timeouts, and filtering to block Slowloris connection-holding attacks at the web interface.

detect

Continuous monitoring of network traffic and resource usage can identify anomalous slow-connection patterns targeting the management web server.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.IR-04 mostly match
prevents

Explicitly requires monitoring and maintaining resource capacity, directly addressing uncontrolled consumption to preserve availability.

DE.CM-09 partial match
prevents

Continuous monitoring of computing resources can detect resource exhaustion but does not itself enforce allocation limits.

PR.IR-03 partial match
prevents

Resilience mechanisms such as avoiding single points of failure indirectly reduce impact of resource exhaustion.

PR.PS-01 partial match
prevents

Hardened configuration baselines can include resource quotas and limits that constrain consumption.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

detects

Resource-utilization monitoring and alerting on bottlenecks or overloads limits the impact of denial-of-service or resource-exhaustion attacks.

prevents

By continuously monitoring utilization, stress-testing peak loads, and maintaining documented plans to scale or throttle resources, the control directly limits an attacker’s ability to drive a system into uncontrolled resource exhaustion.

detects

Pre-agreed severity-based prioritization and resource allocation during incident triage reduce the likelihood that an attacker-induced resource exhaustion will overwhelm the organization before corrective action is taken.

mitigates

Business-continuity plans that include resource-management controls reduce the likelihood that an attacker can trigger uncontrolled resource consumption by forcing the system into a degraded or fallback state.

mitigates

Defining RTOs and capacity requirements for ICT services during business-impact analysis forces organizations to provision sufficient resources and throttling mechanisms, reducing the likelihood that an attacker can induce denial-of-service through uncontrolled resource consumption.

detects

Early notification of anomalous resource consumption or system malfunctions enables throttling or isolation before availability is lost.

References