CVE-2017-16821: b3log Symphony (aka Sym) 2.2.0 has XSS in processor/AdminProcessor.java in the admin console, as demonstrated

Routine

MEDIUM 5.4DOWNGRADE

CVE-2017-16821 is a medium-severity flaw (CVSS 5.4) affecting symphony. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

b3log Symphony (aka Sym) 2.2.0 has XSS in processor/AdminProcessor.java in the admin console, as demonstrated by a crafted X-Forwarded-For HTTP header that is mishandled during display of a client IP address in /admin/user/userid.

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	0.5% (top 59%)
CISA exploited list	No
Weakness	CWE-79
Published	2017-11-15
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: b3log

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

Am I affected?

Timeline

2017-11-15 03:29 UTCPublished CVE record published
2026-06-17 01:09 UTCUpdated Record last modified

b3log symphony DOWNGRADE

Affected: 2.2.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.2.0

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 2.2.0 (Debian / Ubuntu)

apt-cache madison symphony sudo apt install symphony=<VERSION_BEFORE_2.2.0> sudo apt-mark hold symphony

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

dnf --showduplicates list symphony sudo dnf downgrade symphony-<VERSION_BEFORE_2.2.0> sudo dnf versionlock add symphony

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-2017-16821?

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

Is CVE-2017-16821 being exploited?

CVE-2017-16821 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-2017-16821 affect?

CVE-2017-16821 affects symphony. Severity is medium (CVSS 5.4). b3log Symphony (aka Sym) 2.2.0 has XSS in processor/AdminProcessor.java in the admin console, as demonstrated by a crafted X-Forwarded-For HTTP header that is mishandled during display of a client IP address in /admin/user/userid.

How urgent is CVE-2017-16821?

Priority 34/100. Public exploit reference

Software pages

Java vulnerabilities

Related CVEs

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CVE-2020-25343 MEDIUM 5.4 DOWNGRADE Cross-site scripting (XSS) vulnerabilities in Symphony CMS 3.0.0 allow remote attackers to inject arbitrary we
CVE-2020-17405 HIGH 8.8 DOWNGRADE This vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of Se
CVE-2020-15071 MEDIUM 6.1 DOWNGRADE content/content.blueprintsevents.php in Symphony CMS 3.0.0 allows XSS via fields['name'] to appendSubheading.
CVE-2019-9142 MEDIUM 6.1 UPGRADE An issue was discovered in b3log Symphony (aka Sym) before v3.4.7

References

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