CVE-2023-5770Network attack vector

HTML injection via incorrectly encoded email subjects

Published Jan 9, 2024 · Updated Jun 3, 2025

HTML injection in affected Proofpoint Enterprise Protection releases allows remote attackers to alter delivered email bodies through subjects. The email delivery agent rewrites messages before delivery but applies inappropriate output encoding to attacker-controlled subject text, causing embedded HTML to enter the body. Sending a crafted subject requires no authentication; the documented consequence is unauthorized modification of delivered message content.

CVSS severity5.3
Medium
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTML injection in affected Proofpoint Enterprise Protection releases allows remote attackers to alter delivered email bodies through subjects. The email delivery agent rewrites messages before delivery but applies inappropriate output encoding to attacker-controlled subject text, causing embedded HTML to enter the body. Sending a crafted subject requires no authentication; the documented consequence is unauthorized modification of delivered message content.

The record

CVE
CVE-2023-5770
Published
Jan 9, 2024
Updated
Jun 3, 2025
Vendor
Proofpoint
Product
Proofpoint Enterprise Protection
Classifications
CWE-838
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 9, 2024CVE publishedPublication date reported by the CVE source.
  2. Jun 3, 2025Record 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 <8.18.6
  2. Affected versionversion=8.18.6 <patch 4804 changes=[{"at":"patch 4804","status":"unaffected"}]
  3. Affected versionversion=8.20.0 <patch 4805 changes=[{"at":"patch 4805","status":"unaffected"}]
  4. Affected versionversion=8.20.2 <patch 4809 changes=[{"at":"patch 4809","status":"unaffected"}]

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Proofpoint · Proofpoint Enterprise Protectionversion=8.0 <8.18.6; version=8.18.6 <patch 4804 changes=[{"at":"patch 4804","status":"unaffected"}]; version=8.20.0 <patch 4805 changes=[{"at":"patch 4805","status":"unaffected"}]; version=8.20.2 <patch 4809 changes=[{"at":"patch 4809","status":"unaffected"}]

Published CVSS scores

5.4NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
5.3ProofpointCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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 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-838Inappropriate Encoding for Output Context

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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