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CVE Record

CVE-2018-20164: An issue was discovered in regex.yaml (aka regexes.yaml) in UA-Parser UAP-Core before 0.6.0.

An issue was discovered in regex.yaml (aka regexes.yaml) in UA-Parser UAP-Core before 0.6.0. A Regular Expression Denial of Service (ReDoS) issue allows remote attackers to overload a server by setting the User-Agent header in an HTTP(S) request to a value containing a long digit string. (The UAP-Core project contains the vulnerability, propagating to all implementations.)

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This is a denial-of-service weakness in UA-Parser’s shared regex data. A crafted User-Agent header with a long digit sequence can make vulnerable parsers spend excessive CPU, potentially slowing or overloading web services that parse request User-Agent strings.

Executive priority

Treat this as a practical availability risk, not a data-theft issue. Patch exposed services first, especially where User-Agent parsing happens on every request or before traffic controls.

Technical view

CVE-2018-20164 is a ReDoS issue in regex.yaml, also known as regexes.yaml, in UA-Parser UAP-Core before 0.6.0. Because UAP-Core supplies shared regex data, the issue can propagate to downstream implementations that package or consume the vulnerable data.

Likely exposure

Exposure is most likely in internet-facing applications, APIs, logs, analytics, or bot-detection flows that parse HTTP User-Agent headers using UA-Parser UAP-Core data before 0.6.0.

Exploitation context

The provided sources describe remote triggering through an HTTP(S) User-Agent header. There is no KEV listing and no supplied source confirming active exploitation. Practical impact depends on whether User-Agent parsing occurs synchronously on request paths and at what traffic volume.

Researcher notes

The affected component is shared regex data, so language-specific package names may not reveal exposure. Evidence in the bundle does not provide CVSS, CPEs, or active exploitation confirmation; validation should focus on bundled data version and request-path usage.

Mitigation direction

  • Upgrade UA-Parser UAP-Core data to version 0.6.0 or later.
  • Update downstream UA-Parser language packages that bundle vulnerable regex data.
  • Check vendor or package maintainer guidance for implementation-specific fixes.
  • Prioritize services that parse User-Agent headers on public request paths.
  • Review header-size and request-rate controls as compensating protections.

Validation and detection

  • Inventory applications and dependencies that use UA-Parser or UAP-Core data.
  • Confirm bundled regex.yaml or regexes.yaml is from UAP-Core 0.6.0 or later.
  • Check package lockfiles and vendored data copies for older UAP-Core snapshots.
  • Review edge services that parse User-Agent before authentication or rate limiting.
  • Use safe regression tests for parser latency without offensive payload details.
Prepared
Confidence
medium
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

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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
5Source 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

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