CVE-2025-6599· NVD / CVE Program· CNA Zyxel

An uncontrolled resource consumption vulnerability in the web server of Zyxel DX3301-T0 firmware version 5.50(ABVY.6.3)C0 and earlier could

Noroxi assessment

Priority: Monitor (action score 30/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.31% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to CISA the attack is automatable: targets can be found by mass scanning.
According to the record, no fixed version is available yet.
Severity is disputed: the assigning authority (CNA) scores it 5.3, NVD 7.5.

Low priority for now. Update when a fix is released; follow the vendor's advisory.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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

HighCVSS 7.5 · v3.1—No exploit No fix recorded

BDU:2025-16286

Published: Nov 17, 2025
Updated: Jun 17, 2026
EPSS: 0.3% · 22th percentile
CWE: CWE-400

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 30 / 40 · 7.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.3%

CISA SSVC decision

Exploitation: none
Automatable: yes
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 7.5
CNA · Zyxel: 5.3; 2.2 point gap

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
No fixed version yet

If any of these changes, we'll tell you in the daily email digest.

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
zyxel	lte3301-plus firmware	cpe:2.3:o:zyxel:lte3301-plus_firmware
zyxel	lte3301-plus	cpe:2.3:h:zyxel:lte3301-plus
zyxel	nr5103 firmware	cpe:2.3:o:zyxel:nr5103_firmware
zyxel	nr5103	cpe:2.3:h:zyxel:nr5103
zyxel	nr5103e firmware	cpe:2.3:o:zyxel:nr5103e_firmware
zyxel	nr5103e	cpe:2.3:h:zyxel:nr5103e
zyxel	nr5309 firmware	cpe:2.3:o:zyxel:nr5309_firmware
zyxel	nr5309	cpe:2.3:h:zyxel:nr5309
zyxel	nr7302 firmware	cpe:2.3:o:zyxel:nr7302_firmware
zyxel	nr7302	cpe:2.3:h:zyxel:nr7302
zyxel	nr7303 firmware	cpe:2.3:o:zyxel:nr7303_firmware
zyxel	nr7303	cpe:2.3:h:zyxel:nr7303

and 120 more

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

zyxel ax7501-b0 firmwareup to 5.17\(abpc.6.1\)c0 inclusive
zyxel ax7501-b1 firmwareup to 5.17\(abpc.6.1\)c0 inclusive
zyxel dm4200-b0 firmwareup to 5.17\(acbs.1.3\)c0 inclusive
zyxel dx3300-t0 firmwareup to 5.50\(abvy.6.3\)c0 inclusive
zyxel dx3300-t1 firmwareup to 5.50\(abvy.6.3\)c0 inclusive
zyxel dx3301-t0 firmwareup to 5.50\(abvy.6.3\)c0 inclusive
zyxel dx4510-b1 firmwareup to 5.17\(abyl.9\)c0 inclusive
zyxel dx5401-b0 firmwareup to 5.17\(abyo.7\)b2 inclusive
zyxel dx5401-b1 firmwareup to 5.17\(abyo.7\)b2 inclusive
zyxel ee3301-00 firmwareup to 5.63\(acmu.1.1\)c0 inclusive
zyxel ee5301-00 firmwareup to 5.63\(acld.1.1\)c0 inclusive
zyxel ee6510-10 firmwareup to 5.19\(acjq.3\)c0 inclusive
zyxel emg3525-t50b firmwareup to 5.50\(abpm.9.5\)c0 inclusive
zyxel emg5523-t50b firmwareup to 5.50\(abpm.9.5\)c0 inclusive
zyxel emg5723-t50k firmwareup to 5.50\(abom.8.6\)c0 inclusive
zyxel emg6726-b10a firmwareup to 5.13\(abnp.8\)c0 inclusive
zyxel ex3300-t0 firmwareup to 5.50\(abvy.6.3\)c0 inclusive
zyxel ex3300-t0 firmwareup to 5.50\(acdi.2.1\)c0 inclusive
zyxel ex3300-t1 firmwareup to 5.50\(abvy.6.3\)c0 inclusive
zyxel ex3301-t0 firmwareup to 5.50\(abvy.6.3\)c0 inclusive

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Zyxel). Independent of NVD's CPE analysis and usually ahead of it.

Zyxel DX3301-T0 firmware
- <= 5.50(ABVY.6.3)C0affected

Same product

zyxel: all records

Other highest-scoring records for the same primary product.

CVE-2024-8748A buffer overflow vulnerability in the packet parser of the third-party library "libclinkc" in Zyxel VMG8825-T50K firmware versions through
30Monitor
CVE-2022-43392A buffer overflow vulnerability in the parameter of web server in Zyxel NR7101 firmware prior to V1.15(ACCC.3)C0, which could allow an authe
26Monitor
CVE-2022-43391A buffer overflow vulnerability in the parameter of the CGI program in Zyxel NR7101 firmware prior to V1.15(ACCC.3)C0, which could allow an
26Monitor

Published before and after this one in the same product

Later →CVE-2025-11845Feb 23, 2026 · A null pointer dereference vulnerability in the certificate downloader CGI program of the Zyxel VMG3625-T50B firmware versions through 5.50(
19Monitor
Later →CVE-2025-11846Feb 23, 2026 · A null pointer dereference vulnerability in the account settings CGI program of the Zyxel VMG3625-T50B firmware versions through 5.50(ABPM.9
19Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: none
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {2  return node.children.map(expand);3}

Fixed

1const MAX_DEPTH = 32;2function expand(node, depth = 0) {3  if (depth > MAX_DEPTH) throw new Error("too deep");4  return node.children.map((c) => expand(c, depth + 1));5}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

Endpoint Denial of ServiceT1499

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-uncontrolled-resource-consumption-and-command-injection-vulnerabilities-in-certain-4g-lte-5g-nr-cpe-dsl-ethernet-cpe-fiber-onts-security-routers-and-wireless-extenders-11-18-2025

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records