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Date: Sun, 17 Jan 2021 19:31:05 -0000 (UTC)
From: Tavis Ormandy <>
Subject: mutt recipient parsing memory leak

Hello, I noticed mutt was leaking memory whenever I opened a particular
mailbox. I tracked down the problem: Using rfc822 groups without the madatory
labels wasn't being parsed properly.

(A spammer had just put some junk in there, they weren't deliberately using
exotic addressing schemes.. haha).

It turns out that you can send a small message that leaks a *lot* of memory. A
small message can leak GBs of memory, effectively preventing you from opening
your mailbox. You would need to use a different mail client to clean up the
malformed message before you can use mutt again.

I sent this upstream as a DoS, but they don't want to treat it as a security
isssue. I though I'd just send a FYI here instead in case anyone wants to
backport the patch.

Here's the bug with a repro:

Here's the patch:


 _o)            $ lynx
 /\\  _o)  _o)  $ finger
_\_V _( ) _( )  @taviso

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