CVE-2021-21422Public exploitNetwork attack vector

Administrator-session compromise via unescaped document fields

Published Jun 21, 2021 · Updated Aug 3, 2024

Stored cross-site scripting in mongo-express before 1.0.0-alpha.4 allows remote attackers to execute script in an administrator's browser. The oversized-cell preview and media renderers insert document values into HTML without entity-escaping attributes or fetched strings. A remote attacker needs a path to store a crafted database field and an administrator must view or click it; execution can export collections or issue database actions through the administrator session.

CVSS severity6.1
Medium
EPSS probability1.57%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored cross-site scripting in mongo-express before 1.0.0-alpha.4 allows remote attackers to execute script in an administrator's browser. The oversized-cell preview and media renderers insert document values into HTML without entity-escaping attributes or fetched strings. A remote attacker needs a path to store a crafted database field and an administrator must view or click it; execution can export collections or issue database actions through the administrator session.

The record

CVE
CVE-2021-21422
Published
Jun 21, 2021
Updated
Aug 3, 2024
Vendor
mongo-express
Product
mongo-express
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 21, 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=< v1.0.0-alpha.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

mongo-express · mongo-expressversion=< v1.0.0-alpha.4

Published CVSS scores

6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
8.1GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/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 exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007JavaScript/JScript

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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