Security advisory
Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux. A bug was discovered in the `flatpak-portal` service that can allow sandboxed applications to execute arbitrary code on the host system (a sandbox escape). This sandbox-escape bug is present in versions from 0.11.4 and before fixed versions 1.8.5 and 1.10.0. The Flatpak portal D-Bus service (`flatpak-portal`, also known by its D-Bus service name `org.freedesktop.portal.Flatpak`) allows apps in a Flatpak sandbox to launch their own subprocesses in a new sandbox instance, either with the same security settings as the caller or with more restrictive security settings. For example, this is used in Flatpak-packaged web browsers such as Chromium to launch subprocesses that will process untrusted web content, and give those subprocesses a more restrictive sandbox than the browser itself. In vulnerable versions, the Flatpak portal service passes caller-specified environment variables to non-sandboxed processes on the host system, and in particular to the `flatpak run` command that is used to launch the new sandbox instance. A malicious or compromised Flatpak app could set environment variables that are trusted by the `flatpak run` command, and use them to execute arbitrary code that is not in a sandbox. As a workaround, this vulnerability can be mitigated by preventing the `flatpak-portal` service from starting, but that mitigation will prevent many Flatpak apps from working correctly
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2021-21261
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 12:42 UTC · Revision 1
Source evidence
Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux. A bug was discovered in the `flatpak-portal` service that can allow sandboxed applications to execute arbitrary code on the host system (a sandbox escape). This sandbox-escape bug is present in versions from 0.11.4 and before fixed versions 1.8.5 and 1.10.0. The Flatpak portal D-Bus service (`flatpak-portal`, also known by its D-Bus service name `org.freedesktop.portal.Flatpak`) allows apps in a Flatpak sandbox to launch their own subprocesses in a new sandbox instance, either with the same security settings as the caller or with more restrictive security settings. For example, this is used in Flatpak-packaged web browsers such as Chromium to launch subprocesses that will process untrusted web content, and give those subprocesses a more restrictive sandbox than the browser itself. In vulnerable versions, the Flatpak portal service passes caller-specified environment variables to non-sandboxed processes on the host system, and in particular to the `flatpak run` command that is used to launch the new sandbox instance. A malicious or compromised Flatpak app could set environment variables that are trusted by the `flatpak run` command, and use them to execute arbitrary code that is not in a sandbox. As a workaround, this vulnerability can be mitigated by preventing the `flatpak-portal` service from starting, but that mitigation will prevent many Flatpak apps from working correctly
osv:CVE-2021-21261
Complete source record
{
"id": "84a93e10a39a6dc7188ad876a171d76f1da0cee55c729328c3a64fd758a51f1a",
"url": "https://osv.dev/vulnerability/CVE-2021-21261",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "CVE-2021-21261",
"summary": "Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux. A bug was discovered in the `flatpak-portal` service that can allow sandboxed applications to execute arbitrary code on the host system (a sandbox escape). This sandbox-escape bug is present in versions from 0.11.4 and before fixed versions 1.8.5 and 1.10.0. The Flatpak portal D-Bus service (`flatpak-portal`, also known by its D-Bus service name `org.freedesktop.portal.Flatpak`) allows apps in a Flatpak sandbox to launch their own subprocesses in a new sandbox instance, either with the same security settings as the caller or with more restrictive security settings. For example, this is used in Flatpak-packaged web browsers such as Chromium to launch subprocesses that will process untrusted web content, and give those subprocesses a more restrictive sandbox than the browser itself. In vulnerable versions, the Flatpak portal service passes caller-specified environment variables to non-sandboxed processes on the host system, and in particular to the `flatpak run` command that is used to launch the new sandbox instance. A malicious or compromised Flatpak app could set environment variables that are trusted by the `flatpak run` command, and use them to execute arbitrary code that is not in a sandbox. As a workaround, this vulnerability can be mitigated by preventing the `flatpak-portal` service from starting, but that mitigation will prevent many Flatpak apps from working correctly",
"evidence": "osv:CVE-2021-21261",
"products": [],
"severity": "high",
"structured": {
"id": "CVE-2021-21261",
"aliases": [
"CVE-2021-21261",
"GHSA-4ppf-fxf6-vxg2"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/flatpak/flatpak",
"type": "GIT",
"events": [
{
"introduced": "b5571fa0397d1ce0f1aaf9cf6bfe2e60cb90895d"
},
{
"fixed": "58dc0ea96c1648cdec341d7d74c260c3d62eb2bc"
},
{
"introduced": "d395763327116b3b04a8d6d4c33a24074700d2de"
},
{
"fixed": "649ad5fe49945b834da0d616a24400c41666048c"
},
{
"fixed": "6d1773d2a54dde9b099043f07a2094a4f1c2f486"
},
{
"fixed": "6e5ae7a109cdfa9735ea7ccbd8cb79f9e8d3ae8b"
},
{
"fixed": "aeb6a7ab0abaac4a8f4ad98b3df476d9de6b8bd4"
},
{
"fixed": "cc1401043c075268ecc652eac557ef8076b5eaba"
}
],
"database_specific": {
"extracted_events": [
{
"cpe": "cpe:2.3:a:flatpak:flatpak:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "0.11.4"
},
{
"fixed": "1.8.5"
}
],
"source": "CPE_RANGE"
},
{
"cpe": "cpe:2.3:a:flatpak:flatpak:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "1.9.1"
},
{
"fixed": "1.10.0"
}
],
"source": "CPE_RANGE"
},
{
"range": [
{
"fixed": "6d1773d2a54dde9b099043f07a2094a4f1c2f486"
}
],
"source": "REFERENCES_COMMIT"
},
{
"range": [
{
"fixed": "6e5ae7a109cdfa9735ea7ccbd8cb79f9e8d3ae8b"
}
],
"source": "REFERENCES_COMMIT"
},
{
"range": [
{
"fixed": "aeb6a7ab0abaac4a8f4ad98b3df476d9de6b8bd4"
}
],
"source": "REFERENCES_COMMIT"
},
{
"range": [
{
"fixed": "cc1401043c075268ecc652eac557ef8076b5eaba"
}
],
"source": "REFERENCES_COMMIT"
},
{
"range": [
{
"fixed": "58dc0ea96c1648cdec341d7d74c260c3d62eb2bc"
}
],
"source": "REFERENCES_TAG",
"original_tag": "1.8.5"
}
]
}
}
],
"versions": [
"1.8.4",
"1.9.3",
"1.8.3",
"1.9.2",
"1.9.1",
"1.8.2",
"1.8.0",
"1.7.3",
"1.7.2",
"1.7.1",
"1.6.2",
"1.6.1",
"1.6.0",
"1.5.2",
"1.5.1",
"1.5.0",
"1.4.0",
"1.3.4",
"1.3.3",
"1.3.2",
"1.3.1",
"1.3.0",
"1.2.1",
"1.2.0",
"1.1.3",
"1.1.2",
"1.1.1",
"1.1.0",
"1.0.3",
"1.0.2",
"1.0.1",
"1.0.0",
"0.99.3",
"0.99.2",
"0.99.1",
"0.11.8.3",
"0.11.8.2",
"0.11.8.1",
"0.11.8",
"0.11.7",
"0.11.6",
"0.11.5",
"0.11.4"
],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2021-21261.json",
"vanir_signatures": [
{
"id": "CVE-2021-21261-0548202b",
"digest": {
"threshold": 0.9,
"line_hashes": [
"187884336905612395231330406807632357540",
"119966363514582499525315861909166376099",
"46012603303833455347858473125643287427",
"151763468982046354621867926977057407996",
"147841209049247011411836960548228474009",
"210586123448264467490491665920891689504"
]
},
"source": "https://github.com/flatpak/flatpak/commit/6d1773d2a54dde9b099043f07a2094a4f1c2f486",
"target": {
"file": "common/flatpak-bwrap.c"
},
"deprecated": false,
"signature_type": "Line",
"signature_version": "v1"
},
{
"id": "CVE-2021-21261-2cb9cfb5",
"digest": {
"threshold": 0.9,
"line_hashes": [
"168417353790797368165839907690445508493",
"327012681670393743305787150072641325411",
"23688458601150324176395771316217294730",
"49729934599472863566897555018543408450",
"9450908212238931453333786533088716078",
"184028996534785543118806081166217184330",
"141419741360300883951586041005272492896",
"206249337290032327518896842942263903489",
"90318883290108511492839356082770308365",
"12932935097118578644062154051992084777",
"144774528113192030728296602362033592877",
"79201547501775564610540632545667244027",
"268846712764991704531477048056715863846",
"278171116430610011995476595605264549622",
"198046183515048329716552688201140766062",
"186874874185981287271469462079034122186",
"256515148011437925207635412414066159130",
"3346186902999804577361326057752316291",
"254409286826292135473128319948286163718",
"141533511151258764870094348930568640143",
"259454807294067507133633282981503554384",
"191389743288879362348653886153241129053",
"194637151052508142939035967020326419871",
"205972780634195676094809405714121723252",
"23392054317266148780655332786943982622",
"34547951232220976726414035075532117100"
]
},
"source": "https://github.com/flatpak/flatpak/commit/6d1773d2a54dde9b099043f07a2094a4f1c2f486",
"target": {
"file": "common/flatpak-run.c"
},
"deprecated": false,
"signature_type": "Line",
"signature_version": "v1"
},
{
"id": "CVE-2021-21261-33525b89",
"digest": {
"length": 1224,
"function_hash": "116696172303620550801466906987719068366"
},
"source": "https://github.com/flatpak/flatpak/commit/aeb6a7ab0abaac4a8f4ad98b3df476d9de6b8bd4",
"target": {
"file": "portal/flatpak-portal.c",
"function": "child_setup_func"
},
"deprecated": false,
"signature_type": "Function",
"signature_version": "v1"
},
{
"id": "CVE-2021-21261-4a832f75",
"digest": {
"threshold": 0.9,
"line_hashes": [
"181467856496703161714286787676753514560",
"262003444876501901294604323868568402193",
"150489235987664807730600990675707141516",
"308914679741222343840220446431887347020",
"22914194553643468080754179086792170796",
"294736744238137854585260502181037366798",
"257931896619599938072240305823517035948"
]
},
"source": "https://github.com/flatpak/flatpak/commit/6e5ae7a109cdfa9735ea7ccbd8cb79f9e8d3ae8b",
"target": {
"file": "common/flatpak-context.c"
},
"deprecated": false,
"signature_type": "Line",
"signature_version": "v1"
},
{
"id": "CVE-2021-21261-89757ad9",
"digest": {
"length": 4242,
"function_hash": "33047310530798657115268533786732258227"
},
"source": "https://github.com/flatpak/flatpak/commit/6d1773d2a54dde9b099043f07a2094a4f1c2f486",
"target": {
"file": "common/flatpak-run.c",
"function": "flatpak_run_add_environment_args"
},
"deprecated": false,
"signature_type": "Function",
"signature_version": "v1"
},
{
"id": "CVE-2021-21261-cc0442da",
"digest": {
"length": 10642,
"function_hash": "121856444566269508847150148348225191560"
},
"source": "https://github.com/flatpak/flatpak/commit/6d1773d2a54dde9b099043f07a2094a4f1c2f486",
"target": {
"file": "common/flatpak-run.c",
"function": "flatpak_run_app"
},
"deprecated": false,
"signature_type": "Function",
"signature_version": "v1"
},
{
"id": "CVE-2021-21261-e4aba771",
"digest": {
"threshold": 0.9,
"line_hashes": [
"186753914006100194516954110745550884424",
"12753299659279139043630104728458776064",
"269889525867134572535695503617087983501",
"208208283627142296061927458336690996509",
"180501221704741290327491119284995032025",
"176111972974236863265595961229486818247",
"96681180801602239017311502751839799173",
"198705453584377096480089798889685337457"
]
},
"source": "https://github.com/flatpak/flatpak/commit/6d1773d2a54dde9b099043f07a2094a4f1c2f486",
"target": {
"file": "common/flatpak-bwrap-private.h"
},
"deprecated": false,
"signature_type": "Line",
"signature_version": "v1"
},
{
"id": "CVE-2021-21261-f081ded5",
"digest": {
"threshold": 0.9,
"line_hashes": [
"250583380488175601669317137946174719794",
"311312556761816106744451561827799888308",
"296511374797103482356447941591751752716",
"163819300700743363828332066461507542872",
"256646176672544301483717845513293989867",
"283066343764066525662795773450547192544",
"307830766081670044218645905522083376346",
"314613757453546637160749133659371754136",
"33477874074197511545467797114432888206",
"217867266162192291486524756726822760936",
"40016216926295346927460055704050908419",
"202058260553356883764319272044505786272",
"232829783943157726400537389676411531144",
"142269808049044781331577504304469511031",
"228461531246778135043747909129711248394",
"158813393187993092148429072759724546882"
]
},
"source": "https://github.com/flatpak/flatpak/commit/aeb6a7ab0abaac4a8f4ad98b3df476d9de6b8bd4",
"target": {
"file": "portal/flatpak-portal.c"
},
"deprecated": false,
"signature_type": "Line",
"signature_version": "v1"
},
{
"id": "CVE-2021-21261-f0f82716",
"digest": {
"length": 14396,
"function_hash": "138027983890393511308692566048484423621"
},
"source": "https://github.com/flatpak/flatpak/commit/aeb6a7ab0abaac4a8f4ad98b3df476d9de6b8bd4",
"target": {
"file": "portal/flatpak-portal.c",
"function": "handle_spawn"
},
"deprecated": false,
"signature_type": "Function",
"signature_version": "v1"
}
],
"vanir_signatures_modified": "2026-10-20T14:15:20Z"
}
}
],
"modified": "2026-10-20T14:15:20.971945227Z",
"provider": "osv",
"references": [
"https://github.com/flatpak/flatpak/commit/cc1401043c075268ecc652eac557ef8076b5eaba",
"https://github.com/flatpak/flatpak/releases/tag/1.8.5",
"https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2",
"https://security.gentoo.org/glsa/202101-21",
"https://www.debian.org/security/2021/dsa-4830",
"https://github.com/flatpak/flatpak/commit/6d1773d2a54dde9b099043f07a2094a4f1c2f486",
"https://github.com/flatpak/flatpak/commit/6e5ae7a109cdfa9735ea7ccbd8cb79f9e8d3ae8b",
"https://github.com/flatpak/flatpak/commit/aeb6a7ab0abaac4a8f4ad98b3df476d9de6b8bd4"
],
"provider_metadata": {
"unresolved_ranges": [
{
"cpes": [
"cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*"
],
"vendor_product": "debian:debian_linux",
"extracted_events": [
{
"range": [
{
"introduced": "10.0"
},
{
"last_affected": "10.0"
}
],
"source": "CPE_STRING"
}
]
}
]
}
},
"related_cves": [
{
"value": "CVE-2021-21261",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 388772,
"published_at": "2021-01-14T20:15:12.36+00:00"
}