CVE-2021-3539Public exploitNetwork attack vector

Stored XSS via unescaped avatar identifier

Published Aug 4, 2021 · Updated Sep 16, 2024

Stored cross-site scripting in EspoCRM 6.1.6 and earlier allows remote authenticated users to execute script via a crafted avatar ID. The User update API accepts attacker-controlled avatarId text as an image identifier, and avatar rendering inserts it into an HTML attribute without neutralizing quotes or event-handler syntax. Default user rights permit avatar changes, but another user must view the crafted avatar; script then runs in that viewer's EspoCRM session.

CVSS severity6.3
Medium
EPSS probability0.58%
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 EspoCRM 6.1.6 and earlier allows remote authenticated users to execute script via a crafted avatar ID. The User update API accepts attacker-controlled avatarId text as an image identifier, and avatar rendering inserts it into an HTML attribute without neutralizing quotes or event-handler syntax. Default user rights permit avatar changes, but another user must view the crafted avatar; script then runs in that viewer's EspoCRM session.

The record

CVE
CVE-2021-3539
Published
Aug 4, 2021
Updated
Sep 16, 2024
Vendor
EspoCRM
Product
EspoCRM
Classifications
CWE-79, T1189
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 4, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 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=6.1.6 <=6.1.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

EspoCRM · EspoCRMversion=6.1.6 <=6.1.6

Published CVSS scores

3.5NIST NVDAV:N/AC:M/Au:S/C:N/I:P/A:N
5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
6.3Rapid7, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:L/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1189Drive-by Compromise

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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