Vulnerability identifier: #VU15779

Vulnerability risk: Low

CVSSv3.1: 5.5 [CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L/E:U/RL:O/RC:C]

CVE-ID: N/A

CWE-ID: CWE-264

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Steam
Client/Desktop applications / Other client software

Vendor: Valve Software

Description
The vulnerability allows a remote authenticated attacker to bypass security restrictions.

The weakness exists in a Steam web API located at partner.steamgames.com/partnercdkeys/assignkeys/ due to attacker can go through all Steam games IDs, as the appid and keyid parameters were easy to guess. A remote authenticated use the /partnercdkeys/assignkeys/ endpoint on partner.steamgames.com with keycount parameter to "0", bypass the API's limitations, retrieve a file with CD keys belonging to any game and download previously-generated CD keys for a game which they would not normally have access.

Mitigation
Install update from vendor's website.

Vulnerable software versions

Steam: All versions

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External links
http://hackerone.com/reports/391217

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote authenticated user via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.