Security readout for executives and security teams
Plain-English summary
This flaw can corrupt memory when a user interacts with malicious content in affected Microsoft browsers. It requires no attacker account and is listed by CISA as known exploited. Successful exploitation can significantly alter data or system behavior, with lesser confidentiality and availability effects indicated by the CVSS metrics.
Executive priority
Treat this as an immediate high-priority remediation because exploitation is documented and attack complexity is low. Prioritize systems where affected browsers can access untrusted content, then verify update coverage and reduce continued reliance on these products.
Technical view
CVE-2021-26411 is a CWE-416 use-after-free vulnerability affecting Internet Explorer 9, Internet Explorer 11, and EdgeHTML-based Microsoft Edge. Its CVSS 3.1 score is 8.8: network-accessible, low complexity, no privileges required, user interaction required, and changed security scope. The supplied sources do not describe the exploitation mechanism or exact affected builds.
Likely exposure
Exposure exists wherever the affected browser products remain available and can process attacker-controlled content. The supplied version values appear incomplete or unreliable, so they should not define inventory scope. Confirm affected releases and applicable updates against Microsoft’s advisory.
Exploitation context
CISA’s Known Exploited Vulnerabilities catalog supports that this vulnerability has been exploited in the wild. Exploitation still requires user interaction according to the CVSS vector. The supplied evidence provides no campaign details, indicators of compromise, exploit chain, or affected-build boundaries.
Researcher notes
The source bundle identifies CWE-416 but provides no root-cause analysis, exploit details, indicators, fixed build numbers, or campaign attribution. Its listed version strings, including “1.0.0” and “1.0..0,” should not be treated as authoritative product boundaries. Use Microsoft’s advisory for precise applicability.
Mitigation direction
- Review Microsoft’s CVE advisory for applicable product-specific security updates.
- Deploy the applicable Microsoft updates across identified affected systems.
- Eliminate use of affected legacy browser products where operationally feasible.
- Restrict affected browsers from processing untrusted content until remediation is verified.
Validation and detection
- Inventory endpoints for Internet Explorer 9, Internet Explorer 11, and EdgeHTML-based Edge.
- Compare installed update status with Microsoft’s CVE-specific guidance.
- Verify affected browsers are removed, disabled, or updated on exposed endpoints.
- Review browser security telemetry, noting that the supplied sources contain no indicators of compromise.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-416: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-26411 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.8 (3.1)
- Known Exploited
- Yes
- Published
Vector: 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
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CISA KEV status
SSVC decision data
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C2.85.3microsoftVulnerability scoring details
Base CVSS 3.1 score
8.8HighVector: 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
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- Added to KEVCISA-ADP
CISA Known Exploited Vulnerabilities metadata lists this CVE as known exploited.
- ADP timelineCISA-ADP
CVE-2021-26411 added to CISA KEV
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
- 2021-11-03T00:00:00.000Z: CVE-2021-26411 added to CISA KEV
Source materials
- CVE List V5 sourceCVE List V5
- Internet Explorer Memory Corruption VulnerabilityCVE reference, microsoft · vendor-advisory, patch
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26411CVE reference, CVE · x_refsource_MISC, x_transferred
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26411CVE reference, CISA-ADP · government-resource
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.