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NVD / CVE Program· CNA mitre

CVE-2021-42911: A Format String vulnerability exists in DrayTek Vigor 2960 <= 1.5.1.3, DrayTek Vigor 3900 <= 1.5.1.3, and DrayTek Vigor 300B <= 1.5.1.3 in…

CriticalCVSS 9.8 · v3.1—No exploit No fix recorded

Noroxi assessment

Priority: Plan (action score 40/100)

  • 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: 3.5% (FIRST EPSS); higher than 89.4% of all records.
  • 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 the record, no fixed version is available yet.

Add it to your regular patch cycle. 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

A Format String vulnerability exists in DrayTek Vigor 2960 <= 1.5.1.3, DrayTek Vigor 3900 <= 1.5.1.3, and DrayTek Vigor 300B <= 1.5.1.3 in the mainfunction.cgi file via a crafted HTTP message containing malformed QUERY STRING, which could let a remote malicious user execute arbitrary code.

Published
Mar 29, 2022
Updated
Jun 17, 2026
EPSS
3.5% · 89th percentile

Report tools

JSON

Action score

40

Plan

Add it to your regular patch cycle.

CVSS
39 / 40 · 9.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
1 / 30 · 3.5%

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.

Follow CVE-2021-42911

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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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.

VendorProduct
draytekvigor2960 firmware
draytekvigor2960
draytekvigor3900 firmware
draytekvigor3900
draytekvigor300b firmware
draytekvigor300b

Affected versions

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

  • draytek vigor2960 firmwareup to 1.5.1.3 inclusive
  • draytek vigor300b firmwareup to 1.5.1.3 inclusive
  • draytek vigor3900 firmwareup to 1.5.1.3 inclusive

Same product

draytek: all records

Other highest-scoring records for the same primary product.

  • CVE-2020-8515DrayTek Vigor2960 1.3.1_Beta, Vigor3900 1.4.4_Beta, and Vigor300B 1.3.3_Beta, 1.4.2.1_Beta, and 1.4.4_Beta devices allow remote code…KEV
    99Now
  • CVE-2021-43118A Remote Command Injection vulnerability exists in DrayTek Vigor 2960 1.5.1.3, DrayTek Vigor 3900 1.5.1.3, and DrayTek Vigor 300B 1.5.1.3…
    49Plan
  • CVE-2020-19664DrayTek Vigor2960 1.5.1 allows remote command execution via shell metacharacters in a toLogin2FA action to mainfunction.cgi.
    37Monitor

Published before and after this one in the same product

  • Later →CVE-2023-1009Feb 24, 2023 · DrayTek Vigor 2960 Web Management Interface mainfunction.cgi sub_1DF14 path traversal
    27Monitor
  • Later →CVE-2023-24229Mar 15, 2023 · DrayTek Vigor2960 v1.5.1.4 allows an authenticated attacker with network access to the web management interface to inject operating system…
    33Monitor
  • Later →CVE-2023-6265Nov 22, 2023 · DrayTek Vigor2960 mainfunction.cgi dumpSyslog 'option' directory traversal
    33Monitor

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.

Not on record for this CVE: EPSS history · patch commit or PR link · researcher credit · variant or chain candidate · public bounty program.

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
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-134 · Use of Externally-Controlled Format String

CVSS vector

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

nvd-primary

Attack context

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

ATT&CK techniques

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