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CVE Record

CVE-2021-36773: uBlock Origin before 1.36.2 and nMatrix before 4.4.9 support an arbitrary depth of parameter nesting for st...

uBlock Origin before 1.36.2 and nMatrix before 4.4.9 support an arbitrary depth of parameter nesting for strict blocking, which allows crafted web sites to cause a denial of service (unbounded recursion that can trigger memory consumption and a loss of all blocking functionality).

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

A malicious website could make vulnerable browser-blocking extensions consume excessive memory and lose blocking functionality. The business impact is disruption of a user-side security control, not evidence of server compromise or code execution. Exposure is mainly where older uBlock Origin or nMatrix versions remain installed.

Executive priority

Treat this as a hygiene and control-reliability issue. Prioritize managed browser fleets, high-risk users, and Debian-packaged deployments, but do not rank it like a confirmed remote code execution vulnerability based on the provided evidence.

Technical view

CVE-2021-36773 concerns arbitrary-depth parameter nesting in strict blocking handling in uBlock Origin before 1.36.2 and nMatrix before 4.4.9. Crafted sites can trigger unbounded recursion, leading to denial of service, memory consumption, and loss of blocking behavior.

Likely exposure

Organizations are exposed if managed browsers, packaged extensions, or Debian LTS systems still use uBlock Origin before 1.36.2 or nMatrix before 4.4.9. The source bundle does not identify affected CPEs or broader product lines.

Exploitation context

The bundle does not show CISA KEV listing or active exploitation evidence. Public references describe the issue and Debian issued a security update. Practical exposure appears to require an affected extension processing a crafted website.

Researcher notes

Evidence is limited: no CVSS, CWE, CPEs, or KEV signal are provided. Product naming is also slightly inconsistent in the bundle, with the description naming nMatrix while one reference title mentions uMatrix. Do not broaden affected products without vendor confirmation.

Mitigation direction

  • Upgrade uBlock Origin to 1.36.2 or later.
  • Upgrade nMatrix to 4.4.9 or later.
  • Apply Debian LTS ublock-origin security updates where relevant.
  • Check vendor or distro guidance for packaged extension builds.
  • Retire unsupported or unmanaged extension installations.

Validation and detection

  • Inventory browser extension versions across managed endpoints.
  • Check Debian package versions against DLA 3062-1 where applicable.
  • Confirm browser policies prevent outdated extension versions.
  • Review endpoint reports for extension crashes or disabled blocking functionality.
  • Document any systems where update evidence is unavailable.
Prepared
Confidence
medium
Sources
5

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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

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CVE-2021-36773 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

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.

0CVSS vectors
0Timeline events
0ADP providers
4Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.