CVE-2021-26549: An XSS issue was discovered in SmartFoxServer 2.17.0

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MEDIUM 5.4DOWNGRADE

CVE-2021-26549 is a medium-severity flaw (CVSS 5.4) affecting smartfoxserver. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An XSS issue was discovered in SmartFoxServer 2.17.0. Input passed to the AdminTool console is not properly sanitized before being returned to the user. This can be exploited to execute arbitrary HTML code in a user's browser session in context of an affected site.

Why this priority

Public exploit reference

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

Risk facts

CVSS score	5.4 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	Required
EPSS exploit chance	1.3% (top 29%)
CISA exploited list	No
Weakness	CWE-79
Published	2021-02-09
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: smartfoxserver

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

Am I affected?

Timeline

2021-02-09 20:15 UTCPublished CVE record published
2026-06-17 03:43 UTCUpdated Record last modified

smartfoxserver smartfoxserver DOWNGRADE

Affected: 2.17.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.17.0

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 2.17.0 (Debian / Ubuntu)

apt-cache madison smartfoxserver sudo apt install smartfoxserver=<VERSION_BEFORE_2.17.0> sudo apt-mark hold smartfoxserver

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

dnf --showduplicates list smartfoxserver sudo dnf downgrade smartfoxserver-<VERSION_BEFORE_2.17.0> sudo dnf versionlock add smartfoxserver

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-2021-26549?

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

Is CVE-2021-26549 being exploited?

CVE-2021-26549 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-2021-26549 affect?

CVE-2021-26549 affects smartfoxserver. Severity is medium (CVSS 5.4). An XSS issue was discovered in SmartFoxServer 2.17.0. Input passed to the AdminTool console is not properly sanitized before being returned to the user. This can be exploited to execute arbitrary HTML code in a user's browser session in con

How urgent is CVE-2021-26549?

Priority 42/100. Public exploit reference

Related CVEs

CVE-2021-26551 HIGH 8.8 DOWNGRADE An issue was discovered in SmartFoxServer 2.17.0
CVE-2021-26550 MEDIUM 5.5 DOWNGRADE An issue was discovered in SmartFoxServer 2.17.0

References

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