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CVE-2026-1299

Good to know:

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Date: January 23, 2026

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".

Severity Score

Related Resources (11)

https://github.com/python/cpython/commit/0a925ab591c45d6638f37b5e57796f36fa0e56d8
https://github.com/python/cpython/commit/842ce19a0c0b58d61591e8f6a708c38db1fb94e4
https://github.com/python/cpython/commit/052e55e7d44718fe46cbba0ca995cb8fcc359413
https://github.com/python/cpython/commit/8cdf6204f4ae821f32993f8fc6bad0d318f95f36
https://github.com/python/cpython/commit/7877fe424415bc4a13045e62a90a7277413d8cb9
https://github.com/python/cpython/issues/144125
https://github.com/python/cpython/pull/144126
https://nvd.nist.gov/vuln/detail/CVE-2026-1299
https://mail.python.org/archives/list/security-announce@python.org/thread/6ZZULGALJTITEAGEXLDJE2C6FORDXPBT/
https://cve.org/CVERecord?id=CVE-2024-6923
https://www.mend.io/vulnerability-database/CVE-2026-1299

Severity Score

Weakness Type (CWE)

Improper Neutralization of CRLF Sequences ('CRLF Injection')

CWE-93

CVSS v3.1

Base Score:
Attack Vector (AV): NETWORK
Attack Complexity (AC): LOW
Privileges Required (PR): LOW
User Interaction (UI): NONE
Scope (S): UNCHANGED
Confidentiality (C): LOW
Integrity (I): HIGH
Availability (A): NONE

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