CVE-2021-31409Network attack vector

Application denial of service via exponential regex backtracking

Published May 5, 2021 · Updated Sep 17, 2024

Regular expression denial of service in Vaadin Framework 8.0.0 through 8.12.4 allows remote attackers to make applications unresponsive. The com.vaadin.v7.data.validator.EmailValidator pattern applies nested repetition to attacker-controlled domain labels, causing exponential backtracking. Any application that sends untrusted email input to this server-side validator exposes its UI threads; repeated submissions exhaust the thread pool and deny normal use.

CVSS severity7.5
High
EPSS probability1.67%
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 Vaadin Framework 8.0.0 through 8.12.4 allows remote attackers to make applications unresponsive. The com.vaadin.v7.data.validator.EmailValidator pattern applies nested repetition to attacker-controlled domain labels, causing exponential backtracking. Any application that sends untrusted email input to this server-side validator exposes its UI threads; repeated submissions exhaust the thread pool and deny normal use.

The record

CVE
CVE-2021-31409
Published
May 5, 2021
Updated
Sep 17, 2024
Vendor
Vaadin
Product
Vaadin Compatibility Server
Classifications
CWE-400, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 5, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 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=8.0.0 <*

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Vaadin · Vaadin Compatibility Serverversion=8.0.0 <*
Vaadin · Vaadin Frameworkversion=8.0.0 <*

Published CVSS scores

7.5Vaadin Ltd.CVSS: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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.003Application Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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