CVE-2021-21261

Sandbox escape via spawn portal

Published Jan 14, 2021 · Updated Aug 3, 2024

Sandbox escape in Flatpak before 1.8.5 allows local users to execute arbitrary host code via the flatpak-portal D-Bus service. The portal forwards caller-controlled environment variables to the host flatpak run command, allowing a malicious or compromised sandboxed app to inject trusted settings and launch code outside its sandbox. Exploitation requires execution inside a Flatpak sandbox; the resulting impact is host code execution with the privileges available to the portal service.

CVSS severity7.3
High
EPSS probability0.57%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Sandbox escape in Flatpak before 1.8.5 allows local users to execute arbitrary host code via the flatpak-portal D-Bus service. The portal forwards caller-controlled environment variables to the host flatpak run command, allowing a malicious or compromised sandboxed app to inject trusted settings and launch code outside its sandbox. Exploitation requires execution inside a Flatpak sandbox; the resulting impact is host code execution with the privileges available to the portal service.

The record

CVE
CVE-2021-21261
Published
Jan 14, 2021
Updated
Aug 3, 2024
Vendor
Flatpak
Product
Flatpak
Classifications
CWE-74, T1611
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 14, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 0.11.4, < 1.8.5
  2. Affected versionversion=>= 1.9.0, < 1.10.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Flatpak · Flatpakversion=>= 0.11.4, < 1.8.5; version=>= 1.9.0, < 1.10.0

Published CVSS scores

7.3GitHubCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N
7.2NVDAV:L/AC:L/Au:N/C:C/I:C/A:C

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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
T1611Escape to Host

Public exploit references

No public exploit references are available in this record.

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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