CVE-2021-20784Network attack vector

Browser script execution via HTTP header injection

Published Jul 14, 2021 · Updated Dec 3, 2024

HTTP header injection in the Everything 1.0, 1.1, and 1.2 HTTP server allows remote attackers to alter pages or execute scripts. JPCERT/CC identifies the HTTP server as the affected locus but does not disclose which request value reaches which response header or how neutralization fails. Exploitation requires a user to access a website using the affected server, after which attacker-controlled scripting runs in that browser or the displayed page is altered; Lite lacks the HTTP server and is unaffected.

CVSS severity6.1
Medium
EPSS probability1.12%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP header injection in the Everything 1.0, 1.1, and 1.2 HTTP server allows remote attackers to alter pages or execute scripts. JPCERT/CC identifies the HTTP server as the affected locus but does not disclose which request value reaches which response header or how neutralization fails. Exploitation requires a user to access a website using the affected server, after which attacker-controlled scripting runs in that browser or the displayed page is altered; Lite lacks the HTTP server and is unaffected.

The record

CVE
CVE-2021-20784
Published
Jul 14, 2021
Updated
Dec 3, 2024
Vendor
voidtools
Product
Everything
Classifications
CWE-644, T1059.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 14, 2021CVE publishedPublication date reported by the CVE source.
  2. Dec 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=all versions of 1.0 (Everything 1.0 series) except the Lite version
  2. Affected versionversion=all versions of 1.1 (Everything 1.1 series) except the Lite version
  3. Affected versionversion=all versions of 1.2 (Everything 1.2 series) except the Lite version

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

voidtools · Everythingversion=all versions of 1.0 (Everything 1.0 series) except the Lite version; version=all versions of 1.1 (Everything 1.1 series) except the Lite version; version=all versions of 1.2 (Everything 1.2 series) except the Lite version

Published CVSS scores

5.8JPCERT/CCAV:N/AC:M/Au:N/C:P/I:P/A:N
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
6.1JPCERT/CCCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
5.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:N

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-644Improper Neutralization of HTTP Headers for Scripting Syntax
T1059.007Command and Scripting Interpreter: JavaScript

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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