NVD / CVE Program· CNA microsoft

CVE-2021-26411: Internet Explorer Memory Corruption Vulnerability

HighCVSS 8.8 · v3.1KEVWeaponized No fix recorded

Noroxi assessment

Priority: Now (action score 90/100)

CISA has confirmed exploitation in the wild (Nov 3, 2021); it is known to be used in ransomware campaigns. Remediation deadline for US federal agencies: Nov 17, 2021.
Probability of exploitation in the next 30 days: 81.6% (FIRST EPSS); higher than 99.6% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is required. A user must open a link or visit a page. No special conditions are required; it is repeatable.
According to the record, no fixed version is available yet.

Patch today or shut off access. Until a fix is released, restrict access to the affected component and 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 · CISA KEV · FIRST EPSS

BDU:2021-01372

Published: Mar 11, 2021
Updated: Oct 1, 2026
EPSS: 81.6% · 99th percentile
CWE: CWE-416

Report tools

JSON

Action score

Now

Patch today or shut off access.

CVSS: 35 / 40 · 8.8 / 10
CISA KEV: 30 / 30 · Listed
EPSS: 25 / 30 · 81.6%

CISA SSVC decision

Exploitation: active
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · microsoft: 8.8; NVD has not scored this yet; the score shown is the CNA’s.

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Actively exploited in the wild

CISA added this to its Known Exploited Vulnerabilities catalog on Nov 3, 2021. That signals real attacks, not theory.

Remediation deadline for US federal agencies: Nov 17, 2021.

Known to be used in ransomware campaigns.

Get told when this record changes

In CISA KEV: exploitation in the wild confirmed
Weaponized exploit exists
No fixed version yet

If any of these changes, we'll tell you in the daily email digest.

Is your version affected? Check it

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.

We use this product, ask for help

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.

Vendor	Product	CPE
microsoft	edge	cpe:2.3:a:microsoft:edge
microsoft	windows 10 1507	cpe:2.3:o:microsoft:windows_10_1507
microsoft	windows 10 1607	cpe:2.3:o:microsoft:windows_10_1607
microsoft	windows 10 1803	cpe:2.3:o:microsoft:windows_10_1803
microsoft	windows 10 1809	cpe:2.3:o:microsoft:windows_10_1809
microsoft	windows 10 1903	cpe:2.3:o:microsoft:windows_10_1903
microsoft	windows 10 1909	cpe:2.3:o:microsoft:windows_10_1909
microsoft	windows 10 2004	cpe:2.3:o:microsoft:windows_10_2004
microsoft	windows 10 20h2	cpe:2.3:o:microsoft:windows_10_20h2
microsoft	windows server 2016	cpe:2.3:o:microsoft:windows_server_2016
microsoft	windows server 2019	cpe:2.3:o:microsoft:windows_server_2019
microsoft	internet explorer	cpe:2.3:a:microsoft:internet_explorer

and 5 more

Versions reported by the vendor

Affected version ranges reported by the assigning authority (microsoft). Independent of NVD's CPE analysis and usually ahead of it.

Microsoft Internet Explorer 11
- 1.0.0 and later · before 10.0.17134.2087affected
Microsoft Internet Explorer 9
- 1.0.0 and later · before 6.0.6003.21070affected
Microsoft Microsoft Edge (EdgeHTML-based)
- 1.0..0 and later · before 10.0.17134.2087affected

Affected versions

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

microsoft edgeall versions
microsoft internet explorer11
microsoft internet explorer9

Same product

microsoft: all records

Other highest-scoring records for the same primary product.

CVE-2016-7200The Chakra JavaScript scripting engine in Microsoft Edge allows remote attackers to execute arbitrary code or cause a denial of service…KEV
90Now
CVE-2016-7201The Chakra JavaScript scripting engine in Microsoft Edge allows remote attackers to execute arbitrary code or cause a denial of service…KEV
89Now
CVE-2017-0037Microsoft Internet Explorer 10 and 11 and Microsoft Edge have a type confusion issue in the…KEV
86Now

Published before and after this one in the same product

← EarlierCVE-2021-1705Jan 12, 2021 · Microsoft Edge (HTML-based) Memory Corruption Vulnerability
17Monitor
← EarlierCVE-2021-24100Feb 25, 2021 · Microsoft Edge for Android Information Disclosure Vulnerability
21Monitor
Later →CVE-2021-26436Sep 2, 2021 · Microsoft Edge (Chromium-based) Elevation of Privilege Vulnerability
25Monitor

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

Weaponized

A ready exploit tool or active in-the-wild use is known for this vulnerability. This should be your top priority.

Evidence

Proof-of-concept repository on GitHub ×1

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
Source	Kind	Date
Proof-of-concept repository on GitHub	stars:2	2021-11-22

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.

PublishedMar 11, 2021
CISA KEVNov 3, 2021+236 d
First PoCNov 22, 2021+255 d
TodayNov 14, 2026+2073 d

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.
A user must open a link or visit a page.
No special conditions are required; it is repeatable.

If successful

Confidentiality: low · data can be read
Integrity: high · data or configuration can be modified
Availability: low · the service can be disrupted

Impact can extend beyond the vulnerable component (scope changes).

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: Required
Scope: Changed
Confidentiality impact: Low
Integrity impact: High
Availability impact: Low

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

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

nvd-secondary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1free(dev->buf);
2/* ... another thread is still running ... */
3process(dev->buf);

Fixed

1lock(&dev->lock);
2free(dev->buf);
3dev->buf = NULL;
4unlock(&dev->lock);

Attack context

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

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log (0)

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26411

Show all references (2 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records