[exim] [4.94.2] "tainted string" in paniclog in somewhat wei…

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Author: Michal Soltys
Date:  
To: exim-users
Subject: [exim] [4.94.2] "tainted string" in paniclog in somewhat weird circumstance
Hi,

In one of my acl rules I have something like this:

warn
         log_message     = Header syntax invalid [$acl_verify_message], message will be fakerejected
         !verify         = header_syntax
         control         = fakereject/The message will be delivered, but it violates RFCs [$acl_verify_message]. Please fix it.


When we get a message that fails header check, we get exim complaining in paniclog about tainted string (tls connection is also prematurely terminated in such case judging from e.g. msmtp's output, although the mail gets delivered) - removing $acl_verify_message fixes this - but why would this string be considered tainted ?

Is there some way to sanitize it ? I tried using acl_m variable with and without quoting - but it didn't change much.

Example (actual address obfuscated):

2021-07-07 11:38:32.836 1m140m-0001YT-6t Tainted string 'The message will be delivered, but it violates RFCs [malformed address: '>\n may not follow "'mail@???'" <'mail@???: failing address in "To:" header is: "'mail@???'" <'mail@???'>]. Please fix it.' in expansion