CVE
CVE-2021-21206
Google Chromium Blink Use-After-Free Vulnerability
Use after free in Blink in Google Chrome prior to 89.0.4389.128 allowed a remote attacker to potentially exploit heap corruption via a crafted HTML page.
HIGH · CVSS 8.8
⚠ CISA KEV
EPSS 0.1753
Act now
- Listed on CISA KEV (known exploited in the wild)
- SSVC exploitation status: active
- EPSS ≥ 0.10 - elevated exploitation probability
- EPSS percentile: top 5% of all CVEs by exploitation likelihood
- Public exploit or PoC is available
- CVSS base score ≥ 7.0
Sigma rules2
YARA rules0
Look this up elsewhere - one-click external pivots
▸
How to read a CVE - triage first, then detect and patch
This page is every public fact about CVE-2021-21206, cross-linked. Its job is to answer one question fast - does this need my attention now? - and then hand you the two things you do about it. Here is how an analyst reads it.
Triage: should I act now? Four signals, and they are not interchangeable:
CVSSseverity - how bad it is IF exploited, 0-10. A high CVSS alone is not urgency; a flaw can be a perfect 10 and never actually be attacked.
EPSSprobability - a model’s estimate of the chance it is exploited in the next 30 days, 0-1. This is the “will it actually happen” signal.
CISA KEVconfirmed - it is being exploited in the wild right now. The strongest signal on the page; KEV beats any score.
Weaponisedavailability - public exploits / PoCs, and especially Metasploit modules rated Excellent / Great. Reliable, packaged exploit code means low-skill attackers can use it today.
How they combine: KEV, or a dependable Metasploit module, means patch now regardless of CVSS. High CVSS + low EPSS + no exploit is real but not an emergency - schedule it. Low CVSS but KEV-listed still gets patched now. The verdict above already weighed these for you; this is how it got there.
Then what - two workflows:
Detectwhen you cannot patch today, follow this CVE to the ATT&CK techniques it enables, then Build a SIEM detection (the green button) - author a rule, test it in Atomic, deploy it. That buys visibility while the patch waits.
PatchAffected products / packages tell you if you are exposed; Fixed versions by distribution and Vendor advisories give the exact version that closes it.
Reading order for the panels below: verdict + badges, then Public exploits / Metasploit (is it weaponised), then ATT&CK techniques + Sigma / IDS rules (can I detect it), then Affected products / packages + Fixed versions (am I exposed, what patches it), then Threat actors / IOCs (who uses it), then Scoring & timeline / references (the evidence).
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Required Remediation
Apply updates per vendor instructions.
◆
ATT&CK techniques
4Techniques this CVE enables - linked via CWECAPECATT&CK. High◆ = named directly in ATT&CK or Nuclei templates.
T1203 · Exploitation for Client Execution T1566 · Phishing T1059.007 · JavaScript T1203 · Exploitation for Client Execution
▤ Build a SIEM detection for these techniques
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Weakness Classification
CWE-416Use After Free
CWE-416Use After Free
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Affected Products & Versions
2google chrome< 89.0.4389.128
fedoraproject fedoraall versions
⚠
Public Exploits & PoCs
4These PoC and exploit links come from public sources and are not verified to be safe or functional. Review the code before running anything, and treat unverified entries as untrusted.
📦
Fixed versions by distribution
5The package version that resolves this CVE on each Linux distribution, from the vendor’s published security data. fixed in shows a patched version exists; open means the package is listed as affected with no fix yet.
alpine edgechromium fixed in 89.0.4389.128-r0
alpine v3.19chromium fixed in 89.0.4389.128-r0
alpine v3.19qt5-qtwebengine fixed in 5.15.3_git20210510-r0
alpine v3.20chromium fixed in 89.0.4389.128-r0
alpine v3.20qt5-qtwebengine fixed in 5.15.3_git20210510-r0
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Sigma Hunt Rules
2Exact rules name this CVE ID. Product rules name an affected product in their title. Related rules cover techniques used by actors who exploited this CVE. Showing the most relevant matches; the complete related set is on the full drill-down.
producthighRunning Chrome VPN Extensions via the Registry 2 VPN Extension
productmediumPotential Chrome Frame Helper DLL Sideloading
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Scoring & Timeline
8.8
HIGH · CVSS v3.1 · [email protected]
Attack Vector
Network
Adjacent
Local
Physical
Attack Complexity
Low
High
Privileges Required
None
Low
High
User Interaction
None
Required
Scope
Unchanged
Changed
Confidentiality
None
Low
High
Integrity
None
Low
High
Availability
None
Low
High
SSVC triage · cisa-vulnrichment
Exploitation
active
Automatable
no
Technical impact
total
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
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Vendor Advisories
8suse-csafopenSUSE-SU-2024:10681-1
suse-csafopenSUSE-SU-2024:12948-1
suse-csafopenSUSE-SU-2021:0712-1
suse-csafopenSUSE-SU-2021:0575-1
🔗
References & Sources
6Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://security.gentoo.org/glsa/202104-08Third Party Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-21206US Government Resource