Vulnerability identifier: #VU10469

Vulnerability risk: Medium

CVSSv3.1: 5.6 [CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:L/E:H/RL:O/RC:C]

CVE-ID: N/A

CWE-ID: CWE-451

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Telegram Desktop for Windows
Client/Desktop applications / Messaging software

Vendor: Telegram

Description
The vulnerability allows a remote attacker to perform spoofing attack.

The vulnerability exists due to improper parsing of right-to-left override (RLO) character when processing names of the transmitted files in Telegram Desktop for Windows. A remote attacker can create a specially crafted filename with malicious content (e.g. a JavaScript file), disguise it as an image and trick the victim into opening it.

Successful exploitation of the vulnerability may allow an attacker to compromise vulnerable system.

Note: this vulnerability has been exploited in the wild since March until October in 2017, according to Kaspersky Lab and was silently fixed by the vendor.

Mitigation
Update to the latest version. The vulnerability was reported to vendor in October 2017 and fixed afterwards.
It is unclear, in which version this vulnerability was fixed, however according to Kaspersky Lab statement and commits to the official GitHub repository, version 1.1.23 should be vulnerable to this issue.

Vulnerable software versions

Telegram Desktop for Windows: 1.1.23

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External links
http://securelist.com/zero-day-vulnerability-in-telegram/83800/

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

Yes. This vulnerability is being exploited in the wild.