Python CPython up to 3.14.x Email Message BytesGenerator crlf injection

Summaryinfo

A vulnerability, which was classified as problematic, has been found in Python CPython up to 3.14.x. This issue affects the function BytesGenerator of the component Email Message Handler. The manipulation leads to crlf injection. This vulnerability is referenced as CVE-2026-1299. Remote exploitation of the attack is possible. No exploit is available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Python CPython up to 3.14.x. It has been rated as critical. This issue affects the function BytesGenerator of the component Email Message Handler. The manipulation with an unknown input leads to a crlf injection vulnerability. Using CWE to declare the problem leads to CWE-93. The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

The email module, specifically the "BytesGenerator" class, didn’t properly quote newlines for email headers when serializing an email message allowing for header injection when an email is serialized. This is only applicable if using "LiteralHeader" writing headers that don't respect email folding rules, the new behavior will reject the incorrectly folded headers in "BytesGenerator".

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-1299 since 01/21/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 296421 (Linux Distros Unpatched Vulnerability : CVE-2026-1299), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 3.15.0 eliminates this vulnerability. Applying the patch 052e55e7d44718fe46cbba0ca995cb8fcc359413 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (296421) and CERT Bund (WID-SEC-2026-0209). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• Fedora Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• RESF Rocky Linux
• Open Source Python
• Dell Secure Connect Gateway

Productinfo

Type

• Programming Language Software

Vendor

• Python

Name

• CPython

Version

• 3.0
• 3.1
• 3.2
• 3.3
• 3.4
• 3.5
• 3.6
• 3.7
• 3.8
• 3.9
• 3.10
• 3.11
• 3.12
• 3.13
• 3.14

License

• open-source

Website

• Product: https://github.com/python/cpython/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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