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CVE Record

CVE-2021-23364: Regular Expression Denial of Service (ReDoS)

The package browserslist from 4.0.0 and before 4.16.5 are vulnerable to Regular Expression Denial of Service (ReDoS) during parsing of queries.

MediumCVSS 5.3Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Browserslist versions 4.0.0 through before 4.16.5 can spend excessive CPU while parsing specially crafted query text. The business impact is availability only: affected services or build systems could slow down or fail if attackers can influence Browserslist queries.

Executive priority

Treat this as a routine dependency remediation unless Browserslist query parsing is exposed to users or automation inputs. Prioritize normal patch cycles, with faster action for internet-facing services or shared build platforms.

Technical view

CVE-2021-23364 is a Regular Expression Denial of Service issue in browserslist query parsing. The supplied CVSS is 5.3 with network, low-complexity, unauthenticated characteristics and low availability impact. The referenced GitHub PR and commit indicate a code fix was made before 4.16.5.

Likely exposure

Exposure is most relevant where Browserslist parses externally influenced queries at runtime or in automated services. Static, developer-controlled build configuration lowers practical risk. Also check dependency inventories for Java WebJars npm packaging if used.

Exploitation context

The bundle does not show CISA KEV listing or active exploitation. The CVSS vector includes proof-of-concept exploit maturity, but no cited source here establishes real-world attacks.

Researcher notes

The strongest evidence is the package advisory plus upstream PR and commit. Sources identify ReDoS during query parsing and affected versions before 4.16.5. Evidence is incomplete for exploit prevalence, affected deployments, and non-upgrade mitigations.

Mitigation direction

  • Upgrade browserslist to 4.16.5 or later.
  • Regenerate lockfiles so transitive browserslist copies resolve to a fixed version.
  • Check Java WebJars npm dependencies if that packaging is used.
  • If immediate upgrade is blocked, restrict externally supplied Browserslist query input.
  • Monitor vendor and package advisory guidance for any later corrections.

Validation and detection

  • Review SBOMs and lockfiles for browserslist 4.0.0 through 4.16.4.
  • Identify services or jobs that parse Browserslist queries from external input.
  • Confirm installed dependency resolution uses browserslist 4.16.5 or newer.
  • Verify CI and production builds do not retain vulnerable transitive copies.
  • Record whether the WebJars npm package appears in Java dependency manifests.
Prepared
Confidence
high
Sources
6

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-2021-23364 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.3 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:P

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.

1CVSS vectors
0Timeline events
0ADP providers
6Source links

CVSS vector scores

1 official score

We 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.

ScoreVersionSeverityVectorExploitImpactSource
5.3CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:P3.91.4Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

5.3Medium
CVSS 3.1 vector shape for CVE-2021-23364Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:P

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/abrowserslist4.0.0, unspecifiedListed
Weakness

CWE details

No CWE listed

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