CVE-2025-26803: The http parser in Phusion Passenger 6.0.21 through 6.0.25 before 6.0.26 allows a denial of service during par

Routine

MEDIUM 5.3REMOTEUPGRADE

CVE-2025-26803 is a medium-severity flaw (CVSS 5.3) affecting passenger. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The http parser in Phusion Passenger 6.0.21 through 6.0.25 before 6.0.26 allows a denial of service during parsing of a request with an invalid HTTP method.

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 51%)
CISA exploited list	No
Weakness	CWE-908
Published	2025-02-24
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: phusion

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

Am I affected?

Timeline

2025-02-24 16:15 UTCPublished CVE record published
2026-06-17 09:02 UTCUpdated Record last modified

phusion passenger UPGRADE

Affected: >= 6.0.21 and < 6.0.26

Fixed in: 6.0.26

Safe to downgrade to: a release before 6.0.21

1. Check installed version

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

2. UPGRADE to 6.0.26 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade passenger

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 6.0.21 (Debian / Ubuntu)

apt-cache madison passenger sudo apt install passenger=<VERSION_BEFORE_6.0.21> sudo apt-mark hold passenger

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

dnf --showduplicates list passenger sudo dnf downgrade passenger-<VERSION_BEFORE_6.0.21> sudo dnf versionlock add passenger

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-2025-26803?

passenger: upgrade to 6.0.26. Exact commands for each OS are on this page.

Is CVE-2025-26803 being exploited?

CVE-2025-26803 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-2025-26803 affect?

CVE-2025-26803 affects passenger. Severity is medium (CVSS 5.3). The http parser in Phusion Passenger 6.0.21 through 6.0.25 before 6.0.26 allows a denial of service during parsing of a request with an invalid HTTP method.

How urgent is CVE-2025-26803?

Priority 36/100. Remotely exploitable, no login, no user action

References

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