CVE-2020-21493: An issue in the component route\user.php of Xiuno BBS v4.0.4 allows attackers to enumerate usernames.

This week

MEDIUM 5.3REMOTEDOWNGRADE

CVE-2020-21493 is a medium-severity flaw (CVSS 5.3) affecting xiunobbs. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue in the component route\user.php of Xiuno BBS v4.0.4 allows attackers to enumerate usernames.

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.0% (top 37%)
CISA exploited list	No
Published	2021-10-04
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: xiuno

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

Am I affected?

Timeline

2021-10-04 21:15 UTCPublished CVE record published
2026-06-17 03:03 UTCUpdated Record last modified

xiuno xiunobbs DOWNGRADE

Affected: 4.0.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.0.4

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 4.0.4 (Debian / Ubuntu)

apt-cache madison xiunobbs sudo apt install xiunobbs=<VERSION_BEFORE_4.0.4> sudo apt-mark hold xiunobbs

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list xiunobbs sudo dnf downgrade xiunobbs-<VERSION_BEFORE_4.0.4> sudo dnf versionlock add xiunobbs

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-2020-21493?

xiunobbs: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-21493 being exploited?

CVE-2020-21493 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-2020-21493 affect?

CVE-2020-21493 affects xiunobbs. Severity is medium (CVSS 5.3). An issue in the component route\user.php of Xiuno BBS v4.0.4 allows attackers to enumerate usernames.

How urgent is CVE-2020-21493?

Priority 44/100. Public exploit reference; Remotely exploitable, no login, no user action

Software pages

PHP vulnerabilities

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References

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