Buffer overflow in Unix mailer Exim imperils 400,000 email servers

Bug already plugged, get updating


Researchers have uncovered a critical buffer overflow vulnerability in all versions of the Exim mail transfer agent.

The flaw (CVE-2018-6789) leaves an estimated 400,000 email servers at potential risk to remote code execution-style attacks. Fortunately a patched version (Exim version 4.90.1) is already available.

The bug might be exploited by unauthenticated users rather than hackers who have already broken into targeted systems or scored login credentials through some other (doubtless nefarious) means.

Meh Chang, the Taiwanese researcher from the DEVCORE research team who uncovered the flaw, was able to bypass security mitigations built into Exim (such as Address Space Layout Randomisation) in developing a proof-of-concept exploit.

Structure of a handcrafted message capable of exploiting the Exim bug

Structure of a handcrafted message capable of exploiting the Exim bug

The bug stems from (previously dormant) flaws introduced since the first commit of Exim, so all versions prior to the latest update are affected. More details about the vulnerability can be found here.

In an advisory, the developers behind Exim confirmed the development of a patch while playing down the severity of the flaw.

There is a buffer overflow in base64d(), if some pre-conditions are met.

Using a handcrafted message, remote code execution seems to be possible.

A patch exists already and is being tested.

Currently we're unsure about the severity, we *believe*, an exploit is difficult. A mitigation isn't known.

The bug was reported to the Exim team on Monday and they managed to develop and release a fix only two days later.

Another coding error that also represented a remote code execution risk in Exim was discovered and plugged in November. ®

Similar topics


Other stories you might like

  • It's the flu season – FluBot, that is: Surge of info-stealing Android malware detected

    And a bunch of bank-account-raiding trojans also identified

    FluBot, a family of Android malware, is circulating again via SMS messaging, according to authorities in Finland.

    The Nordic country's National Cyber Security Center (NCSC-FI) lately warned that scam messages written in Finnish are being sent in the hope that recipients will click the included link to a website that requests permission to install an application that's malicious.

    "The messages are written in Finnish," the NCSC-FI explained. "They are written without Scandinavian letters (å, ä and ö) and include, for example, the characters +, /, &, % and @ in illogical places in the text to make it more difficult for telecommunications operators to filter the messages. The theme of the text may be that the recipient has received a voicemail message or a message from their mobile operator."

    Continue reading
  • AsmREPL: Wing your way through x86-64 assembly language

    Assemblers unite

    Ruby developer and internet japester Aaron Patterson has published a REPL for 64-bit x86 assembly language, enabling interactive coding in the lowest-level language of all.

    REPL stands for "read-evaluate-print loop", and REPLs were first seen in Lisp development environments such as Lisp Machines. They allow incremental development: programmers can write code on the fly, entering expressions or blocks of code, having them evaluated – executed – immediately, and the results printed out. This was viable because of the way Lisp blurred the lines between interpreted and compiled languages; these days, they're a standard feature of most scripting languages.

    Patterson has previously offered ground-breaking developer productivity enhancements such as an analogue terminal bell and performance-enhancing firmware for the Stack Overflow keyboard. This only has Ctrl, C, and V keys for extra-easy copy-pasting, but Patterson's firmware removes the tedious need to hold control.

    Continue reading
  • Microsoft adds Buy Now, Pay Later financing option to Edge – and everyone hates it

    There's always Use Another Browser

    As the festive season approaches, Microsoft has decided to add "Buy Now, Pay Later" financing options to its Edge browser in the US.

    The feature turned up in recent weeks, first in beta and canary before it was made available "by default" to all users of Microsoft Edge version 96.

    The Buy Now Pay Later (BNPL) option pops up at the browser level (rather than on checkout at an ecommerce site) and permits users to split any purchase between $35 and $1,000 made via Edge into four instalments spread over six weeks.

    Continue reading

Biting the hand that feeds IT © 1998–2021