Pro-Russia hackers target inboxes with 0-day in webmail app used by millions


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A relentless workforce of pro-Russia hackers has been exploiting a zero-day vulnerability in broadly used webmail software program in assaults focusing on governmental entities and a suppose tank, all in Europe, researchers from safety agency ESET mentioned on Wednesday.

The beforehand unknown vulnerability resulted from a crucial cross-site scripting error in Roundcube, a server software utilized by more than 1,000 webmail services and hundreds of thousands of their finish customers. Members of a pro-Russia and Belarus hacking group tracked as Winter Vivern used the XSS bug to inject JavaScript into the Roundcube server software. The injection was triggered just by viewing a malicious electronic mail, which prompted the server to ship emails from chosen targets to a server managed by the menace actor.

No handbook interplay required

“In abstract, by sending a specifically crafted electronic mail message, attackers are in a position to load arbitrary JavaScript code within the context of the Roundcube consumer’s browser window,” ESET researcher Matthieu Faou wrote. “No handbook interplay apart from viewing the message in an online browser is required.”

The assaults started on October 11, and ESET detected them a day later. ESET reported the zero-day vulnerability to Roundcube builders on the identical day, they usually issued a patch on October 14. The vulnerability is tracked as CVE-2023-5631 and impacts Roundcube variations 1.6.x earlier than 1.6.4, 1.5.x earlier than 1.5.5, and 1.4.x earlier than 1.4.15.

Winter Vivern has been working since no less than 2020 and targets governments and suppose tanks, primarily in Europe and Central Asia. In March, the menace group was noticed targeting US government officials who had voiced help for Ukraine in its bid to drive again Russia’s invasion. These assaults additionally exfiltrated targets’ emails however exploited a separate, already-patched XSS in Zimbra Collaboration, a software program package deal that’s additionally used to host webmail portals.

“This actor has been tenacious in its focusing on of American and European officers in addition to army and diplomatic personnel in Europe,” a menace researcher from safety agency Proofpoint mentioned in March when disclosing the assaults exploiting the Zimbra vulnerability. “Since late 2022, [Winter Vivern] has invested an ample period of time learning the webmail portals of European authorities entities and scanning publicly dealing with infrastructure for vulnerabilities all in an effort to in the end achieve entry to emails of these carefully concerned in authorities affairs and the Russia-Ukraine battle.”

The e-mail Winter Vivern used within the latest marketing campaign got here from the handle and had the topic “Get began in your Outlook.”

The email sent in the campaign.

The e-mail despatched within the marketing campaign.

Buried deep within the HTML supply code was a malformed code component often known as an SVG tag. It contained base-64 encoded textual content that, when decoded, translated to JavaScript that contained a command to run within the occasion an error occurred. For the reason that tag contained an intentional error, the malicious command was invoked, and the XSS bug ensured that Roundcube executed the ensuing JavaScript.

HTML source code for the email, with a SVG tag at the end.
Enlarge / HTML supply code for the e-mail, with a SVG tag on the finish.


The ultimate JavaScript payload instructed susceptible servers to checklist folders and emails within the goal’s electronic mail account and to exfiltrate electronic mail messages to an attacker-controlled server by making HTTP requests to https://recsecas[.]com/controlserver/saveMessage.

The final JavaScript payload.
Enlarge / The ultimate JavaScript payload.


Winter Vivern’s earlier success exploiting an already-patched Zimbra vulnerability needs to be a warning. Anybody utilizing Roundcube as both a server admin or an finish consumer ought to make sure the software program is operating a patched model.

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