ATP series firmware: Use of Externally-Controlled Format String
CVE-2023-33011 is a high-severity use of externally-controlled format string vulnerability in ATP series firmware from Zyxel, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited from the same local network by an unauthenticated attacker, without any action from a user. Affected ATP series firmware versions: 5.10 through 5.36 Patch 2. 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
- Update Usg 2200-vpn Firmware to 5.37 or a later version.
- Update Usg Flex 100 Firmware to 5.37 or a later version.
- Update Usg Flex 100w Firmware to 5.37 or a later version.
- Read the advisory on zyxel.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Zyxel | ATP series firmware | 5.10 through 5.36 Patch 2 | Not stated |
| Zyxel | USG FLEX series firmware | 5.00 through 5.36 Patch 2; 5.0.0 through 5.36_patch_2 | Not stated |
| Zyxel | USG FLEX 50(W) series firmware | 5.10 through 5.36 Patch 2; 5.10 through 5.36_patch_2 | Not stated |
| Zyxel | USG20(W)-VPN series firmware | 5.10 through 5.36 Patch 2 | Not stated |
| Zyxel | VPN series firmware | 5.00 through 5.36 Patch 2; 5.00 through 5.36_patch_2 | Not stated |
| Zyxel | atp100_firmware | 5.10 through 5.36_patch_2 | Not stated |
| Zyxel | usg20w-vpn_firmware | 5.10 through 5.36_patch_2 | Not stated |
| Zyxel | Usg 2200-vpn Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Usg Flex 100 Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Usg Flex 100w Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Usg Flex 200 Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Usg Flex 50 Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Usg Flex 500 Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Usg Flex 50w Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Usg Flex 700 Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Zywall Vpn100 Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Zywall Vpn2s Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Zywall Vpn300 Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Zywall Vpn50 Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Zywall VPN 100 Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Zywall VPN 300 Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Zywall VPN 50 Firmware | 5.00 up to, but not including, 5.37 | 5.37 |
| Zyxel | Usg 20w-vpn Firmware | 5.10 up to, but not including, 5.37 | 5.37 |
| Zyxel | Zywall Atp100 Firmware | 5.10 up to, but not including, 5.37 | 5.37 |
| Zyxel | Zywall Atp100w Firmware | 5.10 up to, but not including, 5.37 | 5.37 |
Version data comes from the organisation that assigned the CVE; 4 further products are omitted here. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- AdjacentThe attacker must be on the same local network segment.
- 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
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CNA (zyxel.com.tw).
Official description
A format string vulnerability in the Zyxel ATP series firmware versions 5.10 through 5.36 Patch 2, USG FLEX series firmware versions 5.00 through 5.36 Patch 2, USG FLEX 50(W) series firmware versions 5.10 through 5.36 Patch 2, USG20(W)-VPN series firmware versions 5.10 through 5.36 Patch 2, and VPN series firmware versions 5.00 through 5.36 Patch 2, could allow an unauthenticated, LAN-based attacker to execute some OS commands by using a crafted PPPoE configuration on an affected device when the cloud management mode is enabled.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use of Externally-Controlled Format String
The product uses a function that accepts a format string as an argument, but the format string originates from an external source.
How developers prevent this class of flaw
- Choose a language that is not subject to this flaw.
- Ensure that all format string functions are passed a static string which cannot be controlled by the user, and that the proper number of arguments are always sent to that function as well. If at all possible, use functions that do not support the %n operator in format strings.
- Run compilers and linkers with high warning levels, since they may detect incorrect usage.
More Use of Externally-Controlled Format String vulnerabilities (CWE-134)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other vulnerabilities in ATP series firmware
- 7.2 High severity
- 7.2 High severity
- 8.1 High severity
- 7.2 High severity
- 9.8 Critical severity
Zyxel Multiple Firewalls Path Traversal Exploited
- 7.2 High severity
Recent Use of Externally-Controlled Format String vulnerabilities
- 7.8 High severity
- 9.8 Critical severity
- 7.8 High severity
- 8.8 High severity
- 7.8 High severity
- 8.5 High severity
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