How severe is CVE-2021-42911?

CVE-2021-42911 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-42911 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (87th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-42911?

CVE-2021-42911 primarily affects Draytek Vigor2960 Firmware. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-42911?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-42911 published?

CVE-2021-42911 was published on 2022-03-29 and last updated on 2026-06-17.

CVE-2021-42911

CVE-2021-42911 is a critical-severity vulnerability in Draytek Vigor2960 Firmware with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-134.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 3% (87th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-134
Affected product: Draytek Vigor2960 Firmware
Published: 2022-03-29
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is 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 the mainfunction.cgi file via a crafted HTTP message containing malformed QUERY STRING, which could let a remote malicious user execute arbitrary code.
How severe is CVE-2021-42911?: CVE-2021-42911 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-42911 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (87th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-42911?: CVE-2021-42911 primarily affects Draytek Vigor2960 Firmware. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-42911?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-42911 published?: CVE-2021-42911 was published on 2022-03-29 and last updated on 2026-06-17.

References

https://gist.github.com/Cossack9989/e9c1c2d2e69b773ca4251acdd77f2835

Affected products (3)

cpe:2.3:o:draytek:vigor2960_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:draytek:vigor3900_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:draytek:vigor300b_firmware:*:*:*:*:*:*:*:*

More vulnerabilities in Draytek Vigor2960 Firmware

CVE-2021-43118 — Critical (CVSS 9.8): A Remote Command Injection vulnerability exists in DrayTek Vigor 2960 1.5.1.3, DrayTek Vigor 3900 1.5.1.3, and DrayTek…
CVE-2020-15415 — Critical (CVSS 9.8): On DrayTek Vigor3900, Vigor2960, and Vigor300B devices before 1.5.1, cgi-bin/mainfunction.cgi/cvmcfgupload allows…
CVE-2020-14473 — Critical (CVSS 9.8): Stack-based buffer overflow vulnerability in Vigor3900, Vigor2960, and Vigor300B with firmware before 1.5.1.1.
CVE-2020-14472 — Critical (CVSS 9.8): On Draytek Vigor3900, Vigor2960, and Vigor 300B devices before 1.5.1.1, there are some command-injection…
CVE-2020-14993 — Critical (CVSS 9.8): A stack-based buffer overflow on DrayTek Vigor2960, Vigor3900, and Vigor300B devices before 1.5.1.1 allows remote…
CVE-2020-10828 — Critical (CVSS 9.8): A stack-based buffer overflow in cvmd on Draytek Vigor3900, Vigor2960, and Vigor300B devices before 1.5.1 allows remote…

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Other CWE-134 vulnerabilities

CVE-2012-1851 — Critical (CVSS 10.0): Format string vulnerability in the Print Spooler service in Microsoft Windows XP SP2 and SP3, Windows Server 2003 SP2,…
CVE-2012-0242 — Critical (CVSS 10.0): Format string vulnerability in Advantech/BroadWin WebAccess before 7.0 allows remote attackers to execute arbitrary…
CVE-2011-2475 — Critical (CVSS 10.0): Format string vulnerability in ECTrace.dll in the iMailGateway service in the Internet Mail Gateway in OneBridge Server…
CVE-2011-1568 — Critical (CVSS 10.0): Format string vulnerability in the logText function in shmemmgr9.dll in IGSSdataServer.exe 9.00.00.11074, and…
CVE-2010-4235 — Critical (CVSS 10.0): Format string vulnerability in RealNetworks Helix Server 12.x, 13.x, and 14.x before 14.2, and Helix Mobile Server…
CVE-2011-0270 — Critical (CVSS 10.0): Format string vulnerability in nnmRptConfig.exe in HP OpenView Network Node Manager (OV NNM) 7.51 and 7.53 allows…

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