Zyxel NAS326 firmware: Use of Externally-Controlled Format String
CVE-2022-34747 is a critical-severity use of externally-controlled format string vulnerability in Zyxel NAS326 firmware from Zyxel, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected Zyxel NAS326 firmware versions: < V5.21(AAZF.12)C0. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 1.78% chance of exploitation within 30 days, higher than 79% of scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Nas326 Firmware to 5.21\(aazf.12\)c0 or a later version.
- 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 | Zyxel NAS326 firmware | < V5.21(AAZF.12)C0 | Not stated |
| Zyxel | Nas326 Firmware | before 5.21\(aazf.12\)c0 | 5.21\(aazf.12\)c0 |
Version data comes from the organisation that assigned the CVE. 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
- 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:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.8 | Critical | CNA (zyxel.com.tw) |
| CVSS 3.1 | 9.8 | Critical | NVD |
Official description
A format string vulnerability in Zyxel NAS326 firmware versions prior to V5.21(AAZF.12)C0 could allow an attacker to achieve unauthorized remote code execution via a crafted UDP packet.
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.
- Record last changed materially (score, affected products, status or references).
References
Recent Use of Externally-Controlled Format String vulnerabilities
- 7.8 High severity
- 7.5 High severity
- 7.5 High severity
- 7.8 High severity
- 5.5 Medium severity
- 8.1 High severity
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