CVE-2021-3804Network attack vector

Denial of service via inefficient URL validation regex

Published Sep 17, 2021 · Updated Aug 3, 2024

Inefficient regular expression complexity in NervJS Taro before 3.3.9 allows remote attackers to cause a service hang via crafted URLs. The REG_URL constant in packages/taro-helper/src/constants.ts applies a backtracking-heavy URL-validation expression to attacker-controlled strings, consuming excessive CPU on nonmatching input. No privileges or user interaction are required, and the bounded consequence is loss of availability rather than data disclosure or modification.

CVSS severity7.5
High
EPSS probability1.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Inefficient regular expression complexity in NervJS Taro before 3.3.9 allows remote attackers to cause a service hang via crafted URLs. The REG_URL constant in packages/taro-helper/src/constants.ts applies a backtracking-heavy URL-validation expression to attacker-controlled strings, consuming excessive CPU on nonmatching input. No privileges or user interaction are required, and the bounded consequence is loss of availability rather than data disclosure or modification.

The record

CVE
CVE-2021-3804
Published
Sep 17, 2021
Updated
Aug 3, 2024
Vendor
NervJS
Product
Taro
Classifications
CWE-1333, CAPEC-492, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 17, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <=3.3.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NervJS · Taroversion=unspecified <=3.3.8

Published CVSS scores

7.5GitHub Advisory DatabaseCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1333Inefficient Regular Expression Complexity
CAPEC-492Regular Expression Exponential Blowup
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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