CVE-2021-20777: Improper authorization in handler for custom URL scheme vulnerability in GU App for Android versions from 4.8.

Routine

MEDIUM 4.3UPGRADE

CVE-2021-20777 is a medium-severity flaw (CVSS 4.3) affecting gu. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Improper authorization in handler for custom URL scheme vulnerability in GU App for Android versions from 4.8.0 to 5.0.2 allows a remote attacker to lead a user to access an arbitrary website via the vulnerable App.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.9% (top 41%)
CISA exploited list	No
Weakness	CWE-862
Published	2021-07-07
Last modified	2026-06-17

Publisher (CNA): JPCERT/CC · Vendor: gu-global

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

Am I affected?

Timeline

2021-07-07 08:15 UTCPublished CVE record published
2026-06-17 03:34 UTCUpdated Record last modified

gu-global gu UPGRADE

Affected: >= 4.8.0 and <= 5.0.2

Fixed in: newer than 5.0.2

Safe to downgrade to: a release before 4.8.0

1. Check installed version

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

2. UPGRADE to newer than 5.0.2 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade gu

Note

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

3. If no update is available yet, DOWNGRADE to a release before 4.8.0 (Debian / Ubuntu)

apt-cache madison gu sudo apt install gu=<VERSION_BEFORE_4.8.0> sudo apt-mark hold gu

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list gu sudo dnf downgrade gu-<VERSION_BEFORE_4.8.0> sudo dnf versionlock add gu

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

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-2021-20777?

gu: upgrade to newer than 5.0.2. Exact commands for each OS are on this page.

Is CVE-2021-20777 being exploited?

CVE-2021-20777 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-2021-20777 affect?

CVE-2021-20777 affects gu. Severity is medium (CVSS 4.3). Improper authorization in handler for custom URL scheme vulnerability in GU App for Android versions from 4.8.0 to 5.0.2 allows a remote attacker to lead a user to access an arbitrary website via the vulnerable App.

How urgent is CVE-2021-20777?

Priority 30/100. No elevated risk signals yet.

Software pages

Android vulnerabilities

References

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