CVE-2019-18409: The ruby_parser-legacy (aka legacy) gem 1.0.0 for Ruby allows local privilege escalation because of world-writ

Routine

HIGH 7.8DOWNGRADE

CVE-2019-18409 is a high-severity flaw (CVSS 7.8) affecting ruby parser-legacy. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The ruby_parser-legacy (aka legacy) gem 1.0.0 for Ruby allows local privilege escalation because of world-writable files. For example, if the brakeman gem (which has a legacy dependency) 4.5.0 through 4.7.0 is used, a local user can insert malicious code into the ruby_parser-legacy-1.0.0/lib/ruby_parser/legacy/ruby_parser.rb file.

Why this priority

High severity
Public exploit reference

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

Risk facts

CVSS score	7.8 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.3% (top 74%)
CISA exploited list	No
Weakness	CWE-732
Published	2019-10-24
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: zenspider

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

Am I affected?

Timeline

2019-10-24 14:15 UTCPublished CVE record published
2026-06-17 02:24 UTCUpdated Record last modified

zenspider ruby parser-legacy DOWNGRADE

Affected: 1.0.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.0.0

1. Check installed version

apt-cache policy ruby-parser-legacy || rpm -q ruby-parser-legacy || ruby-parser-legacy --version

2. No fixed release: DOWNGRADE to a release before 1.0.0 (Debian / Ubuntu)

apt-cache madison ruby-parser-legacy sudo apt install ruby-parser-legacy=<VERSION_BEFORE_1.0.0> sudo apt-mark hold ruby-parser-legacy

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

dnf --showduplicates list ruby-parser-legacy sudo dnf downgrade ruby-parser-legacy-<VERSION_BEFORE_1.0.0> sudo dnf versionlock add ruby-parser-legacy

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-2019-18409?

ruby parser-legacy: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2019-18409 being exploited?

CVE-2019-18409 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-2019-18409 affect?

CVE-2019-18409 affects ruby parser-legacy. Severity is high (CVSS 7.8). The ruby_parser-legacy (aka legacy) gem 1.0.0 for Ruby allows local privilege escalation because of world-writable files. For example, if the brakeman gem (which has a legacy dependency) 4.5.0 through 4.7.0 is used, a local user can insert

How urgent is CVE-2019-18409?

Priority 39/100. High severity; Public exploit reference

Software pages

Ruby vulnerabilities

References

← Back to latest CVEs