CVE-2021-32802 [Critical] | Security Vulnerability in Nextcloud Server

Nextcloud server is an open source, self hosted personal cloud. Nextcloud supports rendering image previews for user provided file content. For some image types, the Nextcloud server was invoking a third-party library that wasn't suited for untrusted user-supplied content. There are several security concerns with passing user-generated content to this library, such as Server-Side-Request-Forgery, file disclosure or potentially executing code on the system. The risk depends on your system configuration and the installed library version. It is recommended that the Nextcloud Server is upgraded to 20.0.12, 21.0.4 or 22.1.0. These versions do not use this library anymore. As a workaround users may disable previews by setting `enable_previews` to `false` in `config.php`.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-07-01	2.52%	2.60%	+0.08%
2	2026-06-15	2.25%	2.52%	+0.27%
3	2026-03-04	—	2.25%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-07-01

2.52%

2.60%

+0.08%

2026-06-15

2.25%

2.52%

+0.27%

2026-03-04

—

2.25%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
9.3	3.1	CRITICAL	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:L` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:C) Breaking this can reach past the original component and bite other resources—bigger blast radius. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:L) Might cause slowdowns, glitches, or partial disruption—not a full brick.	3.9	4.7	[email protected]
9.8	3.1	CRITICAL	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	5.9	[email protected]
10.0	2.0	HIGH	`AV:N/AC:L/Au:N/C:C/I:C/A:C` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:N) No authentication is required. Confidentiality impact (C:C) Complete confidentiality impact. Integrity impact (I:C) Complete integrity impact. Availability impact (A:C) Complete availability impact.	10.0	10.0	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

9.3

3.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:L Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C): Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:L): Might cause slowdowns, glitches, or partial disruption—not a full brick.

3.9

4.7

[email protected]

9.8

3.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

3.9

5.9

[email protected]

10.0

2.0

HIGH

AV:N/AC:L/Au:N/C:C/I:C/A:C Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:C): Complete confidentiality impact.
Integrity impact (I:C): Complete integrity impact.
Availability impact (A:C): Complete availability impact.

10.0

[email protected]

OS Trackers for CVE-2021-32802

vendor	priority	summary	link
`gentoo`	low	CVE-2021-32802: 1 GLSA(s) (202208-17), 1 atom(s) (www-apps/nextcloud); latest impact low.	https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-32802

Affected software / configurations for CVE-2021-32802

Vendor	Product	Version	Raw CPE
nextcloud	nextcloud_server	< 20.0.12	cpe:2.3:a:nextcloud:nextcloud_server::::::::
nextcloud	nextcloud_server	>= 21.0.0, < 21.0.4	cpe:2.3:a:nextcloud:nextcloud_server::::::::
nextcloud	nextcloud_server	>= 22.0.0, < 22.1.0	cpe:2.3:a:nextcloud:nextcloud_server::::::::

References for CVE-2021-32802

URL	Tags
https://docs.nextcloud.com/server/21/admin_manual/configuration_files/previews_configuration.html#disabling-previews	Vendor Advisory
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-m682-v4g9-wrq7	Mitigation Third Party Advisory
https://hackerone.com/reports/1261413	Permissions Required Third Party Advisory
https://security.gentoo.org/glsa/202208-17	Third Party Advisory

URL

CVE-2021-32802 | Preview generation used third-party library not suited for user-generated content in Nextcloud server

Exploit prediction scoring system (EPSS) score for CVE-2021-32802

Common vulnerability scoring system (CVSS) metrics for CVE-2021-32802

Weakness enumeration for CVE-2021-32802

OS Trackers for CVE-2021-32802

Affected software / configurations for CVE-2021-32802

References for CVE-2021-32802