CVE-2021-33502Public exploitNetwork attack vector

Application hang via data URL regex backtracking

Published May 24, 2021 · Updated Aug 3, 2024

ReDoS in normalize-url 4.3.0 through 4.5.0, 5.0.0 through 5.3.0, and 6.0.0 allows remote attackers to hang applications. The normalizeDataURL function applies overlapping lazy wildcard groups to the media type, payload, and optional fragment, causing exponential regex backtracking on crafted data URLs. Exposure requires an application to pass attacker-controlled data URLs to the library; CPU exhaustion then blocks the Node.js event loop and interrupts service.

CVSS severity7.5
High
EPSS probability1.70%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

ReDoS in normalize-url 4.3.0 through 4.5.0, 5.0.0 through 5.3.0, and 6.0.0 allows remote attackers to hang applications. The normalizeDataURL function applies overlapping lazy wildcard groups to the media type, payload, and optional fragment, causing exponential regex backtracking on crafted data URLs. Exposure requires an application to pass attacker-controlled data URLs to the library; CPU exhaustion then blocks the Node.js event loop and interrupts service.

The record

CVE
CVE-2021-33502
Published
May 24, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-1333, CWE-400, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 24, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitPublished

Weakness, pattern, technique

CWE-1333Inefficient Regular Expression Complexity
CWE-400Uncontrolled Resource Consumption
T1499.004Application or System Exploitation

Public exploit references

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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