CVE-2024-6923 in CPython
Summary
by MITRE • 08/01/2024
There is a MEDIUM severity vulnerability affecting CPython.
The email module didn’t properly quote newlines for email headers when serializing an email message allowing for header injection when an email is serialized.
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Analysis
by VulDB Data Team • 11/01/2025
The vulnerability identified as CVE-2024-6923 represents a medium severity issue within the CPython email module that fundamentally compromises the integrity of email header serialization processes. This flaw specifically manifests when the email module fails to properly quote newlines during the serialization of email messages, creating a condition that enables header injection attacks. The vulnerability exists in the core email handling functionality of Python's standard library, making it a critical concern for applications that process or generate email content.
The technical implementation of this vulnerability stems from inadequate handling of special characters, particularly newlines, within email header fields during the serialization phase. When email headers contain unescaped newline characters, the serialization process does not properly quote these characters according to RFC standards for email header formatting. This improper quoting creates opportunities for attackers to inject additional headers or manipulate existing header values by inserting malicious newline sequences that break the expected header structure. The flaw operates at the protocol level where email headers are constructed and serialized, making it particularly dangerous in contexts where user input is processed without proper sanitization.
From an operational impact perspective, this vulnerability enables attackers to perform header injection attacks that can lead to various security consequences including email spoofing, spam relay abuse, and potential data exfiltration through manipulated email headers. Applications using the affected email module may inadvertently allow attackers to inject malicious headers that could redirect email traffic, modify message routing, or even inject commands in certain email processing environments. The medium severity classification reflects the fact that exploitation requires specific conditions but can result in significant compromise of email communication integrity and potentially broader system security implications.
Organizations should implement immediate mitigations including updating to patched versions of CPython where available, implementing additional input validation for email headers, and ensuring proper sanitization of user-provided content before email processing. The vulnerability aligns with CWE-115 which describes improper handling of special characters in email headers, and represents a variant of techniques documented in ATT&CK matrix under T1192 for email spoofing and T1071 for application layer protocol manipulation. Security teams should monitor their email processing applications for potential exploitation attempts and consider implementing email header validation as part of their defensive measures. The fix typically involves ensuring that newline characters are properly escaped or quoted during the email header serialization process to prevent injection attacks.