How severe is CVE-2021-27705?

CVE-2021-27705 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-2021-27705 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (85th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-27705?

CVE-2021-27705 primarily affects Tenda G1 Firmware. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-27705?

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-2021-27705 published?

CVE-2021-27705 was published on 2021-04-14 and last updated on 2026-06-17.

CVE-2021-27705

CVE-2021-27705 is a critical-severity vulnerability in Tenda G1 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-120.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 3% (85th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-120
Affected product: Tenda G1 Firmware
Published: 2021-04-14
Last modified: 2026-06-17

Description

Buffer Overflow in Tenda G1 and G3 routers with firmware v15.11.0.17(9502)_CN allows remote attackers to execute arbitrary code via a crafted action/"qosIndex "request. This occurs because the "formQOSRuleDel" function directly passes the parameter "qosIndex" to strcpy without limit.

Frequently asked questions

What is CVE-2021-27705?: Buffer Overflow in Tenda G1 and G3 routers with firmware v15.11.0.17(9502)_CN allows remote attackers to execute arbitrary code via a crafted action/"qosIndex "request. This occurs because the "formQOSRuleDel" function directly passes the parameter "qosIndex" to strcpy without limit.
How severe is CVE-2021-27705?: CVE-2021-27705 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-2021-27705 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (85th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-27705?: CVE-2021-27705 primarily affects Tenda G1 Firmware. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-27705?: 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-2021-27705 published?: CVE-2021-27705 was published on 2021-04-14 and last updated on 2026-06-17.

References

https://hackmd.io/Zb7lfFaNR0ScpaTssECFbg

Affected products (2)

cpe:2.3:o:tenda:g1_firmware:v15.11.0.17\(9502\)_cn:*:*:*:*:*:*:*
cpe:2.3:o:tenda:g3_firmware:v15.11.0.17\(9502\)_cn:*:*:*:*:*:*:*

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CVE-2021-27707 — Critical (CVSS 9.8): Buffer Overflow in Tenda G1 and G3 routers with firmware v15.11.0.17(9502)_CN allows remote attackers to execute…
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