CVE-2020-26304Public exploitNetwork attack vector

Browser crash via exponential URL regex backtracking

Published Oct 26, 2024 · Updated Oct 28, 2024

Regular expression denial of service in ZURB Foundation for Sites 6.6.3 and earlier allows attackers to crash browsers via crafted URL input. Three URL-validation regular expressions use ambiguous overlapping repetitions that force exponential backtracking on a long nonmatching URL. The browser hang requires a user to paste the crafted value or a site to prefill attacker-controlled input; no data access or modification is reported.

CVSS severity8.7
High
EPSS probability0.54%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Regular expression denial of service in ZURB Foundation for Sites 6.6.3 and earlier allows attackers to crash browsers via crafted URL input. Three URL-validation regular expressions use ambiguous overlapping repetitions that force exponential backtracking on a long nonmatching URL. The browser hang requires a user to paste the crafted value or a site to prefill attacker-controlled input; no data access or modification is reported.

The record

CVE
CVE-2020-26304
Published
Oct 26, 2024
Updated
Oct 28, 2024
Vendor
ZURB
Product
Foundation for Sites
Classifications
CWE-1333, CAPEC-492, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 26, 2024CVE publishedPublication date reported by the CVE source.
  2. Oct 28, 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=0 <=6.6.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ZURB · Foundation for Sitesversion=0 <=6.6.3

Published CVSS scores

8.7GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/U:Green
7.5NIST NVDCVSS:3.1/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 exploitPublished

Weakness, pattern, technique

CWE-1333Inefficient Regular Expression Complexity
CAPEC-492Regular Expression Exponential Blowup
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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