CVE-2019-5420

A remote code execution vulnerability in development mode Rails <5.2.2.1, <6.0.0.beta3 can allow an attacker to guess the automatically generated development mode secret token. This secret token can be used in combination with other Rails internals to escalate to a remote code execution exploit.

CVSS: 9.8Critical
Exploited in the wild: Not knownPublic exploit code; not in CISA KEV
EPSS: 89.3%chance of exploitation in the next 30 daystop 0.3% of scored CVEsFIRST score of 11 Nov 2026
Fix: Patch availablesee the advisories in the references
Published: 27 Mar 2019analysed here 12 Nov 2026

Summary

Triage

Attack surface: Server-side
Exploitable: Runtime and configuration
Attack vector: network
Weaknesses: CWE-77 Command Injection
CWE-330 Use of Insufficiently Random Values
Can a WAF block it?: Partly. See why

The summary, impact and action text on this page are written by our AI analysis pipeline, or taken from the NVD description when a CVE was imported from NVD. They are not the vendor's wording: check them against the sources. A longer AI executive summary and technical analysis are generated for signed-in accounts on the Max plan.

Affected products

Product	Affected versions	Vendor says fixed in
Rails https://github.com/rails/rails	5.2.2.16.0.0.beta3Vendor says fixed in: not stated	Not stated by the vendor

As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.

Products named in our analysis

rubyonrails:rails
debian:debian_linux
fedoraproject:fedora

Fix and mitigation

WAF and other mitigations

Can a WAF block it? Partly. Command injection puts shell syntax into the request. WAF rules catch common shell commands but miss encoded or unusual payloads.

Also consider: input validation · RASP · CSPRNG

Based on the weakness type only; no CVE-specific evidence yet. We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.

Remediation steps (AI-written)

Step-by-step remediation is generated for accounts on the Max plan, for CVEs that match a technology in their stack. Add this technology to your stack to see the fix checklist.

Exploitation evidence

CISA KEV catalog: Not listed as of our last sync.
Public exploit code: Yes: 1 on Exploit-DB · 1 Metasploit module · 12 GitHub proofs of concept

Exploit-DB

Ruby On Rails - DoubleTap Development Mode secret_key_base Remote Code Execution (Metasploit)remote, 2 May 2019, verified by Exploit-DB

Metasploit

exploit/multi/http/rails_double_tapexploit, rank excellent

GitHub proofs of concept

and 8 more repositories

Listed so you can judge urgency, not as a recommendation to run anything. GitHub “proofs of concept” are unvetted: some are fake or carry malware. Exploit-DB marks the entries its staff verified.

Timeline

21 Mar 2019First public exploit or proof of concept
27 Mar 2019Published7 days later
4 Aug 2024CVE record last updated1,957 days (about 5 years) later
12 Nov 2026Analysed by vulneraibility.com830 days (about 2 years) later

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Metric	Value	What it means
Attack vector	NetworkReachable over the internet or any routable network.	Reachable over the internet or any routable network.
Attack complexity	LowRepeatable attack, no special conditions.	Repeatable attack, no special conditions.
Privileges required	NoneThe attacker needs no prior access.	The attacker needs no prior access.
User interaction	NoneNo victim action needed.	No victim action needed.
Scope	UnchangedImpact stays within the vulnerable component.	Impact stays within the vulnerable component.
Confidentiality	HighTotal data disclosure possible.	Total data disclosure possible.
Integrity	HighComplete modification possible.	Complete modification possible.
Availability	HighFull outage possible.	Full outage possible.

Common questions

Is CVE-2019-5420 being exploited?

Not confirmed. CVE-2019-5420 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 89% probability of exploitation in the next 30 days.

How severe is CVE-2019-5420?

CVE-2019-5420 is rated Critical with a CVSS score of 9.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.

Is there a patch for CVE-2019-5420?

Yes. A fix has been recorded for CVE-2019-5420. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.

What does CVE-2019-5420 affect?

CVE-2019-5420 affects rubyonrails:rails, debian:debian_linux, fedoraproject:fedora. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.

Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.

References

NVD CVE.org CVE Details Source

5 references in the CVE record, grouped by the tags the record gives them.

Advisories (1)

lists.fedoraproject.org /archives/list/package-announce%40lists.fedoraproject.org/message/Y43636TH4D6T46

Exploits (1)

exploit-db.com /exploits/46785/

Where the data on this page comes from

CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
NVD: CVSS and CPE data
FIRST EPSS: exploit probability and percentile
Exploit-DB: published exploits
Metasploit Framework: exploit and scanner modules
PoC-in-GitHub: GitHub repositories that claim a proof of concept

Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.

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