CVE-2023-5770VulnerabilityPublished 9 Jan 2024Updated 3 Jun 2025

CVE-2023-5770: Proofpoint Enterprise Protection · Inappropriate Encoding for Output Context

Affects Proofpoint Enterprise ProtectionSource CVE Database V5

Not known to be exploited · CVSS 5.3 Medium.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 27% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 9 Jan 2024
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Proofpoint Proofpoint Enterprise Protection	Affected =8.20.2 =8.20.0 =8.18.6 =8.0	Fixed in–

AI-suggested

Organizations should immediately verify their Proofpoint Enterprise Protection version and apply the latest patches (4804, 4805, 4809 or later) provided by Proofpoint to remediate this vulnerability. In addition to patching, administrators should implement strict email content filtering policies that detect and block suspicious HTML content, especially in email subjects and bodies. Deploying advanced threat protection solutions that analyze email behavior and content can help identify exploitation attempts. Regularly auditing email gateway logs for anomalous patterns or injection attempts is recommended. User awareness training focused on recognizing phishing and suspicious email content remains critical. Network segmentation and limiting exposure of email gateway management interfaces reduce attack surface. Finally, organizations should monitor threat intelligence feeds for any emerging exploits targeting this vulnerability and be prepared to respond promptly.

Description

Proofpoint Enterprise Protection contains a vulnerability in the email delivery agent that allows an unauthenticated attacker to inject improperly encoded HTML into the email body of a message through the email subject. The vulnerability is caused by inappropriate encoding when rewriting the email before delivery.This issue affects Proofpoint Enterprise Protection: from 8.20.2 before patch 4809, from 8.20.0 before patch 4805, from 8.18.6 before patch 4804 and all other prior versions.

Impact

For European organizations, this vulnerability poses a significant risk to email security and trustworthiness. Proofpoint Enterprise Protection is widely deployed in enterprises and government agencies across Europe to filter and protect email communications. Exploitation could allow attackers to craft emails that appear legitimate but contain malicious HTML content, potentially facilitating phishing campaigns, credential theft, or delivery of further malware payloads. This undermines the integrity of email communications and could lead to data breaches or financial fraud. Given the critical role of email in business operations and regulatory compliance (e.g., GDPR), such manipulation could also result in reputational damage and legal consequences. The medium severity rating reflects that while direct system compromise is unlikely, the indirect effects on organizational security posture and user trust are considerable. Organizations relying on Proofpoint for email filtering must be vigilant, as attackers could leverage this vulnerability to bypass security controls and target European users with sophisticated social engineering attacks.

CWE-838Inappropriate Encoding for Output Context (opens in a new tab)
Base weakness
The product uses or specifies an encoding when generating output to a downstream component, but the specified encoding is not the same as the encoding that is expected by the downstream component.
Implementation · Output Encoding
Use context-aware encoding. That is, understand which encoding is being used by the downstream component, and ensure that this encoding is used. If an encoding can be specified, do so, instead of assuming that the default encoding is the same as the default being assumed by the downstream component.
Architecture and Design · Output Encoding
Where possible, use communications protocols or data formats that provide strict boundaries between control and data. If this is not feasible, ensure that the protocols or formats allow the communicating components to explicitly state which encoding/decoding method is being used.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
OWASP Cheat Sheets
Content Security Policy (opens in a new tab)
OWASP ASVS 4.0.3
V14.4.6 (opens in a new tab)
V14.4.4 (opens in a new tab)
V14.4.2 (opens in a new tab)
Attack patterns
Generic Cross-Browser Cross-Domain Theft (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

proofpoint.com/us/security/security-advisories/pfpt-sa-2023-0009 (opens in a new tab)

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 4 Jul 2025, 08:27 UTC

WeaknessesCWE-838

Technical details

References

Community reviews

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