Strip CR/LF from SMTP subjects derived from event data - #4258
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Strip CR/LF from SMTP subjects derived from event data#4258shaggyinsomniac wants to merge 1 commit into
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The SmtpAppender subject is produced by a PatternLayout serializer and commonly embeds event data (message, MDC, throwable). CR/LF sequences in that data flow into MimeMessage.setSubject unsanitized, allowing mail header injection when an attacker can influence logged content (for example a 'Bcc' header relayed through the application's SMTP credentials). Strip CR and LF from subjects in MimeMessageBuilder.setSubject and in the SmtpManager multipart send paths of both the javax (log4j-core) and jakarta (log4j-jakarta-smtp) modules. Signed-off-by: Sagar Chanchal <Sagarr2112@gmail.com>
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Description
The
SmtpAppendersubject is produced by a PatternLayout serializer and commonly embeds event data (message, MDC, throwable). CR/LF sequences in that data currently flow intoMimeMessage.setSubjectunsanitized, allowing mail header injection when an attacker can influence logged content — for example a logged username or error message containing\r\nBcc: attacker@example.comresults in an injectedBccheader relayed through the application's SMTP credentials.This strips CR and LF from the subject in:
MimeMessageBuilder.setSubject(log4j-coreandlog4j-jakarta-smtp)SmtpManagervariantsTesting
MimeMessageBuilderTest(new): asserts a plain subject round-trips unchanged, and a subject containing CRLF has all CR/LF removed (making the remainder inert text within the single subject value). Both pass; no other behavior changes.