CVE-2021-30481Public exploitNetwork attack vector

Code execution via invite-triggered buffer overflow

Published Apr 10, 2021 · Updated Nov 3, 2025

Buffer overflow in Valve Steam before 2021-04-17 allows remote authenticated users to execute arbitrary code through a crafted Steam invite. The public record identifies invite handling as the locus but does not disclose the affected function, buffer, or unchecked copy operation. Exploitation requires a Source engine game to be installed and the recipient to click the invite, after which attacker-supplied code runs in the game process.

CVSS severity9.0
Critical
EPSS probability3.50%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in Valve Steam before 2021-04-17 allows remote authenticated users to execute arbitrary code through a crafted Steam invite. The public record identifies invite handling as the locus but does not disclose the affected function, buffer, or unchecked copy operation. Exploitation requires a Source engine game to be installed and the recipient to click the invite, after which attacker-supplied code runs in the game process.

The record

CVE
CVE-2021-30481
Published
Apr 10, 2021
Updated
Nov 3, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-120, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 10, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

8.0MITRECVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:H
6.0NVDAV:N/AC:M/Au:S/C:P/I:P/A:P
9.0NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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