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Vulnerability Details :

CVE-2026-39971

Summary
Assigner-GitHub_M
Assigner Org ID-a0819718-46f1-4df5-94e2-005712e83aaa
Published At-14 Apr, 2026 | 23:35
Updated At-15 Apr, 2026 | 16:22
Rejected At-
Credits

Serendipity: Host Header Injection leads to SMTP header injection via unvalidated HTTP_HOST

Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the email sending functionality in include/functions.inc.php inserts $_SERVER['HTTP_HOST'] directly into the Message-ID SMTP header without validation, and the existing sanitization function serendipity_isResponseClean() is not called on HTTP_HOST before embedding it. An attacker who can control the Host header during an email-triggering action such as comment notifications or subscription emails can inject arbitrary SMTP headers into outgoing emails. This enables identity spoofing, reply hijacking via manipulated Message-ID threading, and email reputation abuse through the attacker's domain being embedded in legitimate mail headers. This issue has been fixed in version 2.6.0.

Vendors
-
Not available
Products
-
Metrics (CVSS)
VersionBase scoreBase severityVector
Weaknesses
Attack Patterns
Solution/Workaround
References
HyperlinkResource Type
EPSS History
Score
Latest Score
-
N/A
No data available for selected date range
Percentile
Latest Percentile
-
N/A
No data available for selected date range
Stakeholder-Specific Vulnerability Categorization (SSVC)
▼Common Vulnerabilities and Exposures (CVE)
cve.org
Assigner:GitHub_M
Assigner Org ID:a0819718-46f1-4df5-94e2-005712e83aaa
Published At:14 Apr, 2026 | 23:35
Updated At:15 Apr, 2026 | 16:22
Rejected At:
▼CVE Numbering Authority (CNA)
Serendipity: Host Header Injection leads to SMTP header injection via unvalidated HTTP_HOST

Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the email sending functionality in include/functions.inc.php inserts $_SERVER['HTTP_HOST'] directly into the Message-ID SMTP header without validation, and the existing sanitization function serendipity_isResponseClean() is not called on HTTP_HOST before embedding it. An attacker who can control the Host header during an email-triggering action such as comment notifications or subscription emails can inject arbitrary SMTP headers into outgoing emails. This enables identity spoofing, reply hijacking via manipulated Message-ID threading, and email reputation abuse through the attacker's domain being embedded in legitimate mail headers. This issue has been fixed in version 2.6.0.

Affected Products
Vendor
s9y
Product
Serendipity
Versions
Affected
  • < 2.6.0
Problem Types
TypeCWE IDDescription
CWECWE-113CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')
Type: CWE
CWE ID: CWE-113
Description: CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')
Metrics
VersionBase scoreBase severityVector
3.17.2HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Version: 3.1
Base score: 7.2
Base severity: HIGH
Vector:
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Metrics Other Info
Impacts
CAPEC IDDescription
Solutions
Configurations
Workarounds
Exploits
Credits
Timeline
EventDate
Replaced By
Rejected Reason
References
HyperlinkResource
https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r
x_refsource_CONFIRM
https://github.com/s9y/Serendipity/releases/tag/2.6.0
x_refsource_MISC
Hyperlink: https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r
Resource:
x_refsource_CONFIRM
Hyperlink: https://github.com/s9y/Serendipity/releases/tag/2.6.0
Resource:
x_refsource_MISC
▼Authorized Data Publishers (ADP)
CISA ADP Vulnrichment
Affected Products
Metrics
VersionBase scoreBase severityVector
Metrics Other Info
Impacts
CAPEC IDDescription
Solutions
Configurations
Workarounds
Exploits
Credits
Timeline
EventDate
Replaced By
Rejected Reason
References
HyperlinkResource
Information is not available yet
▼National Vulnerability Database (NVD)
nvd.nist.gov
Source:security-advisories@github.com
Published At:15 Apr, 2026 | 04:17
Updated At:23 Apr, 2026 | 13:59

Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the email sending functionality in include/functions.inc.php inserts $_SERVER['HTTP_HOST'] directly into the Message-ID SMTP header without validation, and the existing sanitization function serendipity_isResponseClean() is not called on HTTP_HOST before embedding it. An attacker who can control the Host header during an email-triggering action such as comment notifications or subscription emails can inject arbitrary SMTP headers into outgoing emails. This enables identity spoofing, reply hijacking via manipulated Message-ID threading, and email reputation abuse through the attacker's domain being embedded in legitimate mail headers. This issue has been fixed in version 2.6.0.

CISA Catalog
Date AddedDue DateVulnerability NameRequired Action
N/A
Date Added: N/A
Due Date: N/A
Vulnerability Name: N/A
Required Action: N/A
Metrics
TypeVersionBase scoreBase severityVector
Secondary3.17.2HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Type: Secondary
Version: 3.1
Base score: 7.2
Base severity: HIGH
Vector:
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
CPE Matches
s9y
s9y
>>serendipity>>Versions before 2.6.0(exclusive)
cpe:2.3:a:s9y:serendipity:*:*:*:*:*:*:*:*
s9y
s9y
>>serendipity>>2.6.0
cpe:2.3:a:s9y:serendipity:2.6.0:beta1:*:*:*:*:*:*
Weaknesses
CWE IDTypeSource
CWE-113Primarysecurity-advisories@github.com
CWE ID: CWE-113
Type: Primary
Source: security-advisories@github.com
Evaluator Description
Evaluator Impact

Evaluator Solution

Vendor Statements
References
HyperlinkSourceResource
https://github.com/s9y/Serendipity/releases/tag/2.6.0security-advisories@github.com
Patch
https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6rsecurity-advisories@github.com
Exploit
Vendor Advisory
Mitigation
Hyperlink: https://github.com/s9y/Serendipity/releases/tag/2.6.0
Source: security-advisories@github.com
Resource:
Patch
Hyperlink: https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r
Source: security-advisories@github.com
Resource:
Exploit
Vendor Advisory
Mitigation

Change History

0
Information is not available yet

Similar CVEs

1Records found
CVE-2023-26137
Matching Score-4
Assigner-Snyk
ShareView Details
Matching Score-4
Assigner-Snyk
CVSS Score-7.2||HIGH
EPSS-0.43% / 35.61%
||
7 Day CHG~0.00%
Published-06 Jul, 2023 | 05:00
Updated-19 Nov, 2024 | 18:56
Rejected-Not Available
Known To Be Used In Ransomware Campaigns?-Not Available
KEV Added-Not Available
KEV Action Due Date-Not Available

All versions of the package drogonframework/drogon are vulnerable to HTTP Response Splitting when untrusted user input is used to build header values in the addHeader and addCookie functions. An attacker can add the \r\n (carriage return line feeds) characters to end the HTTP response headers and inject malicious content.

Action-Not Available
Vendor-drogonn/a
Product-drogondrogonframework/drogon
CWE ID-CWE-113
Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')
CWE ID-CWE-444
Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Details not found