CVE-2018-8899: IdentityServer IdentityServer4 1.x before 1.5.3 and 2.x before 2.1.3 does not encode the redirect URI on the a

Routine

MEDIUM 6.1UPGRADE

CVE-2018-8899 is a medium-severity flaw (CVSS 6.1) affecting identityserver4. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

IdentityServer IdentityServer4 1.x before 1.5.3 and 2.x before 2.1.3 does not encode the redirect URI on the authorization response page, which might lead to XSS in some configurations.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	1.2% (top 31%)
CISA exploited list	No
Weakness	CWE-79
Published	2018-03-22
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: identityserver

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

Am I affected?

Timeline

2018-03-22 05:29 UTCPublished CVE record published
2026-06-17 02:05 UTCUpdated Record last modified

identityserver identityserver4 UPGRADE

Affected: >= 1.0.0 and <= 1.5.2 · >= 2.0.0 and <= 2.1.2

Fixed in: newer than 2.1.2

Safe to downgrade to: a release before 1.0.0

1. Check installed version

apt-cache policy identityserver4 || rpm -q identityserver4 || identityserver4 --version

2. UPGRADE to newer than 2.1.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade identityserver4

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade identityserver4

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 1.0.0 (Debian / Ubuntu)

apt-cache madison identityserver4 sudo apt install identityserver4=<VERSION_BEFORE_1.0.0> sudo apt-mark hold identityserver4

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

dnf --showduplicates list identityserver4 sudo dnf downgrade identityserver4-<VERSION_BEFORE_1.0.0> sudo dnf versionlock add identityserver4

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-2018-8899?

identityserver4: upgrade to newer than 2.1.2. Exact commands for each OS are on this page.

Is CVE-2018-8899 being exploited?

CVE-2018-8899 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-2018-8899 affect?

CVE-2018-8899 affects identityserver4. Severity is medium (CVSS 6.1). IdentityServer IdentityServer4 1.x before 1.5.3 and 2.x before 2.1.3 does not encode the redirect URI on the authorization response page, which might lead to XSS in some configurations.

How urgent is CVE-2018-8899?

Priority 38/100. No elevated risk signals yet.

Related CVEs

CVE-2019-12250 MEDIUM 6.1 UPGRADE IdentityServer IdentityServer4 through 2.4 has stored XSS via the httpContext to the host/Extensions/RequestLo

References

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