CVE-2021-34823: The ON24 ScreenShare (aka DesktopScreenShare.app) plugin before 2.0 for macOS allows remote file access via it

Q: How do I fix CVE-2021-34823?

screenshare: upgrade to 2.0. Exact commands for each OS are on this page.

Q: Is CVE-2021-34823 being exploited?

CVE-2021-34823 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-34823 affect?

CVE-2021-34823 affects screenshare. Severity is critical (CVSS 9.1). The ON24 ScreenShare (aka DesktopScreenShare.app) plugin before 2.0 for macOS allows remote file access via its built-in HTTP server. This allows unauthenticated remote users to retrieve files accessible to the logged-on macOS user. When a

Q: How urgent is CVE-2021-34823?

Priority 57/100. Critical severity; Remotely exploitable, no login, no user action

This month

CRITICAL 9.1REMOTEUPGRADE

CVE-2021-34823 is a critical-severity flaw (CVSS 9.1) affecting screenshare. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The ON24 ScreenShare (aka DesktopScreenShare.app) plugin before 2.0 for macOS allows remote file access via its built-in HTTP server. This allows unauthenticated remote users to retrieve files accessible to the logged-on macOS user. When a remote user sends a crafted HTTP request to the server, it triggers a code path that will download a configuration file from a specified remote machine over HTTP. There is an XXE flaw in processing of this conf

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.0% (top 19%)
CISA exploited list	No
Weakness	CWE-611
Published	2021-08-13
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: on24

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-08-13 17:15 UTCPublished CVE record published
2026-06-17 03:56 UTCUpdated Record last modified

on24 screenshare UPGRADE

Affected: < 2.0

Fixed in: 2.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy screenshare || rpm -q screenshare || screenshare --version

2. UPGRADE to 2.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade screenshare

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade screenshare

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-34823?

screenshare: upgrade to 2.0. Exact commands for each OS are on this page.

Is CVE-2021-34823 being exploited?

CVE-2021-34823 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-34823 affect?

CVE-2021-34823 affects screenshare. Severity is critical (CVSS 9.1). The ON24 ScreenShare (aka DesktopScreenShare.app) plugin before 2.0 for macOS allows remote file access via its built-in HTTP server. This allows unauthenticated remote users to retrieve files accessible to the logged-on macOS user. When a

How urgent is CVE-2021-34823?

Priority 57/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

macOS vulnerabilities

References

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