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Exploited vulnerability · CISA KEV

Is CVE-2021-31755 exploited? Yes: in CISA KEV since 3 Nov 2021

Gociux · Tenda AC11 Router · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2021-31755, Tenda AC11 Router Stack Buffer Overflow Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 3 Nov 2021, 180 days after it was published. It affects Tenda AC11 Router. If you run it, CISA's required action is: Apply updates per vendor instructions.

exploitedYesCISA KEV · 3 Nov 2021
ransomwareNot knownno confirmed use
EPSStop 1%among the most likely CVEs to be exploited
severity9.8CVSS 3.1 · critical
US federal due17 Nov 2021BOD 22-01 deadline

What it is

Tenda AC11 devices contain a stack buffer overflow vulnerability in /goform/setmac which allows attackers to execute code via a crafted post request.

VendorTenda (3 exploited CVEs in KEV)
ProductAC11 Router
VulnerabilityTenda AC11 Router Stack Buffer Overflow Vulnerability
WeaknessCWE-787
Published7 May 2021
Added to KEV3 Nov 2021
Reported by (CNA)mitre

What to do

  1. Check whether you run it. Look for AC11 Router in your asset inventory, including appliances and cloud images. Stack check lists every exploited Tenda CVE at once.
  2. Apply the fix. Apply updates per vendor instructions.
  3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 7 May 2021.
  4. Get told next time. Email alerts when CISA adds a CVE for Tenda.

References

Questions

Is CVE-2021-31755 being exploited?

Yes. CISA added CVE-2021-31755 to the Known Exploited Vulnerabilities catalog on 3 Nov 2021, which means there is reliable evidence of exploitation in the wild.

Is CVE-2021-31755 used in ransomware attacks?

CISA does not list known ransomware use for it. That can change, and exploitation alone is reason to fix it first.

How do I fix CVE-2021-31755?

Apply updates per vendor instructions. Check Tenda's advisory for the fixed versions, and if you can't patch quickly, restrict access to the affected AC11 Router and watch it for signs of compromise.

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in November 2021 · Tenda scorecard · act-now radar.

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