Valve Steam before 2021-04-17, when a Source engine game is installed, allows remote authenticated users to execute arbitrary code because…

published 2021-04-10 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-17404

cvss: 8.0; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 3.5%; EPSS 3.5% chance of exploitation in 30 days, percentile 89%
public exploits: 0; none known

Valve Steam before 2021-04-17, when a Source engine game is installed, allows remote authenticated users to execute arbitrary code because of a buffer overflow that occurs for a Steam invite after one click.

Exploit prediction

3.53% chance of exploitation in the next 30 days, higher than 89% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

twitter.com https://twitter.com/the_secret_club/status/1380868759129296900 referenced PoC, tagged "exploit" by a source, unverified
youtube.com https://www.youtube.com/watch?v=rNQn--9xR1Q referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	3.1	8.0	CVSS:3.1/AC:H/AV:N/A:H/C:H/I:H/PR:L/S:C/UI:R
CNA	3.1	8.0	CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:H
NVD	3.1	9.0	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H
NVD	2.0	6.0	AV:N/AC:M/Au:S/C:P/I:P/A:P

Classification

Weakness

CWE-120 Buffer Copy without Checking Size of Input

References

twitter.com /the_secret_club/status/1380868759129296900
exploit, third-party-advisory
youtube.com /watch?v=rNQn--9xR1Q
exploit, third-party-advisory
news.ycombinator.com /item?id=26762170
issue-tracking, third-party-advisory
twitter.com /floesen_/status/1337107178096881666
third-party-advisory

Sources

CVE List CVE-2021-30481
NVD CVE-2021-30481

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary