DX3301-T0 firmware: Uncontrolled Resource Consumption
CVE-2025-6599 is a high-severity uncontrolled resource consumption vulnerability in DX3301-T0 firmware from Zyxel, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected DX3301-T0 firmware versions: <= 5.50(ABVY.6.3)C0. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.34% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of DX3301-T0 firmware you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on zyxel.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Zyxel | DX3301-T0 firmware | <= 5.50(ABVY.6.3)C0 | Not stated |
| Zyxel | Lte3301-plus Firmware | 1.00\(abqu.7\)c0 and earlier | Not stated |
| Zyxel | Nr5103 Firmware | 4.19\(abyc.8\)c0 and earlier | Not stated |
| Zyxel | Nr5103e Firmware | 1.00\(acdj.1\)c0 and earlier | Not stated |
| Zyxel | Nr5309 Firmware | 1.00\(ackp.1\)b3 and earlier | Not stated |
| Zyxel | Nr7302 Firmware | 5.00\(acha.5\)c0 and earlier | Not stated |
| Zyxel | Nr7303 Firmware | 1.00\(acei.1\)c0 and earlier | Not stated |
| Zyxel | Nebula Fwa505 Firmware | 1.19\(acko.0\)c0 and earlier | Not stated |
| Zyxel | Nebula Fwa510 Firmware | 1.20\(acgd.1\)c0 and earlier | Not stated |
| Zyxel | Nebula Fwa515 Firmware | 1.50\(acpz.0\)c0 and earlier | Not stated |
| Zyxel | Nebula Fwa710 Firmware | 1.20\(acgc.0\)c0 and earlier | Not stated |
| Zyxel | Dm4200-b0 Firmware | 5.17\(acbs.1.3\)c0 and earlier | Not stated |
| Zyxel | Dx3300-t0 Firmware | 5.50\(abvy.6.3\)c0 and earlier | Not stated |
| Zyxel | Dx3300-t1 Firmware | 5.50\(abvy.6.3\)c0 and earlier | Not stated |
| Zyxel | Dx4510-b1 Firmware | 5.17\(abyl.9\)c0 and earlier | Not stated |
| Zyxel | Dx5401-b0 Firmware | 5.17\(abyo.7\)b2 and earlier | Not stated |
| Zyxel | Dx5401-b1 Firmware | 5.17\(abyo.7\)b2 and earlier | Not stated |
| Zyxel | Ee3301-00 Firmware | 5.63\(acmu.1.1\)c0 and earlier | Not stated |
| Zyxel | Ee5301-00 Firmware | 5.63\(acld.1.1\)c0 and earlier | Not stated |
| Zyxel | Ee6510-10 Firmware | 5.19\(acjq.3\)c0 and earlier | Not stated |
| Zyxel | Ex3300-t0 Firmware | 5.50\(abvy.6.3\)c0 and earlier; 5.50\(acdi.2.1\)c0 and earlier | Not stated |
| Zyxel | Ex3300-t1 Firmware | 5.50\(abvy.6.3\)c0 and earlier | Not stated |
| Zyxel | Ex3301-t0 Firmware | 5.50\(abvy.6.3\)c0 and earlier | Not stated |
| Zyxel | Ex3500-t0 Firmware | 5.44\(achr.4\)c0 and earlier | Not stated |
| Zyxel | Ex3501-t0 Firmware | 5.44\(achr.4\)c0 and earlier | Not stated |
Version data comes from the organisation that assigned the CVE; 35 further products are omitted here. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 5.3 | Medium | CNA (zyxel.com.tw) |
| CVSS 3.1 | 7.5 | High | NVD |
Official description
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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Uncontrolled Resource Consumption
The product does not properly control the allocation and maintenance of a limited resource.
How developers prevent this class of flaw
- Ensure that protocols have specific limits of scale placed on them.
- Ensure that all failures in resource allocation place the system into a safe posture.
More Uncontrolled Resource Consumption vulnerabilities (CWE-400)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Other vulnerabilities in DX3301-T0 firmware
- 7.2 High severity
- 8.8 High severity
- 8.8 High severity
- 7.2 High severity
- 7.2 High severity
- 7.5 High severity
Recent Uncontrolled Resource Consumption vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 8.7 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
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