CVE-2019-18978: An issue was discovered in the rack-cors (aka Rack CORS Middleware) gem before 1.0.4 for Ruby

Q: How do I fix CVE-2019-18978?

rack-cors: upgrade to 1.0.4; debian linux: mitigate or apply the listed mitigation; ubuntu linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2019-18978 being exploited?

CVE-2019-18978 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2019-18978 affect?

CVE-2019-18978 affects rack-cors, debian linux, ubuntu linux. Severity is medium (CVSS 5.3). An issue was discovered in the rack-cors (aka Rack CORS Middleware) gem before 1.0.4 for Ruby. It allows ../ directory traversal to access private resources because resource matching does not ensure that pathnames are in a canonical format.

Q: How urgent is CVE-2019-18978?

Priority 50/100. Remotely exploitable, no login, no user action; On your watchlist

This month

MEDIUM 5.3REMOTEWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2019-18978 is a medium-severity flaw (CVSS 5.3) affecting rack-cors, debian linux, ubuntu linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue was discovered in the rack-cors (aka Rack CORS Middleware) gem before 1.0.4 for Ruby. It allows ../ directory traversal to access private resources because resource matching does not ensure that pathnames are in a canonical format.

Why this priority

Remotely exploitable, no login, no user action
On your watchlist

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	2.5% (top 16%)
CISA exploited list	No
Weakness	CWE-22
Published	2019-11-14
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: canonical · debian · rack-cors project

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

Am I affected?

Timeline

2019-11-14 21:15 UTCPublished CVE record published
2026-06-17 02:25 UTCUpdated Record last modified

rack-cors project rack-cors UPGRADE

Affected: < 1.0.4

Fixed in: 1.0.4

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy rack-cors || rpm -q rack-cors || rack-cors --version

2. UPGRADE to 1.0.4 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade rack-cors

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade rack-cors

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

debian debian linux MITIGATE

Affected: 8.0 · 9.0 · 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

canonical ubuntu linux MITIGATE

Affected: 16.04

Fixed in: no fixed release known

Safe to downgrade to: a release before 16.04

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

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-2019-18978?

rack-cors: upgrade to 1.0.4; debian linux: mitigate or apply the listed mitigation; ubuntu linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2019-18978 being exploited?

CVE-2019-18978 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-2019-18978 affect?

CVE-2019-18978 affects rack-cors, debian linux, ubuntu linux. Severity is medium (CVSS 5.3). An issue was discovered in the rack-cors (aka Rack CORS Middleware) gem before 1.0.4 for Ruby. It allows ../ directory traversal to access private resources because resource matching does not ensure that pathnames are in a canonical format.

How urgent is CVE-2019-18978?

Priority 50/100. Remotely exploitable, no login, no user action; On your watchlist

Software pages

Ubuntu vulnerabilities · Debian vulnerabilities · Ruby vulnerabilities

Related CVEs

CVE-2017-11173 HIGH 8.8 UPGRADE MITIGATE Missing anchor in generated regex for rack-cors before 0.4.1 allows a malicious third-party site to perform CO

References

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