CVE-2019-16254

Ruby through 2.4.7, 2.5.x through 2.5.6, and 2.6.x through 2.6.4 allows HTTP Response Splitting. If a program using WEBrick inserts untrusted input into the response header, an attacker can exploit it to insert a newline character to split a header, and inject malicious content to deceive clients. NOTE: this issue exists because of an incomplete fix for CVE-2017-17742, which addressed the CRLF vector, but did not address an isolated CR or an isolated LF.

Published: 2019-11-26 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2019-16254 is rated Moderate Risk (53/100): CVSS Medium severity, with high exploitation likelihood (EPSS 4.57%, 90th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2019-16254

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-19 4.45% 4.57% +0.12%
2 2026-06-15 0.71% 4.45% +3.74%
3 2026-03-04 — 0.71% —

Full EPSS history (49 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2019-16254

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 1.4 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2019-16254

OS Trackers for CVE-2019-16254

vendor priority summary link
alpine medium CVE-2019-16254: 1 source package rows (ruby); 30 state rows across 10 repos (3.10-main, 3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 10, open 20. https://security.alpinelinux.org/vuln/CVE-2019-16254
debian not yet assigned CVE-2019-16254 not yet assigned priority: Debian including 1 source packages (jruby), 4 status rows across 4 suites (bookworm, forky, sid, trixie): resolved 4. https://security-tracker.debian.org/tracker/CVE-2019-16254
gentoo normal CVE-2019-16254: 1 GLSA(s) (202003-06), 1 atom(s) (dev-lang/ruby); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2019-16254
redhat low — https://access.redhat.com/security/cve/CVE-2019-16254
suse medium CVE-2019-16254 severity moderate: SUSE including 311 source package names (2.17-17.3:libruby2_5-2_5-2.5.7-4.8.1, 2.17-17.3:ruby2.5-2.5.7-4.8.1, …), 1053 product×package rows across 270 product lines (Container bci/ruby, Container suse/rmt-server, … (270 product lines)): Fixed 860, Known Affected 157, Known Not Affected 30, Will Not Fix 6. https://www.suse.com/security/cve/CVE-2019-16254/
ubuntu medium CVE-2019-16254 medium priority: Ubuntu including 3 source packages (jruby, ruby2.3, ruby2.5), 32 status rows across 11 suites (bionic, disco, eoan, focal, groovy, hirsute, impish, jammy, trusty, upstream, xenial): DNE 16, not-affected 7, released 6, needs-triage 2, ignored 1. https://ubuntu.com/security/CVE-2019-16254

Affected software / configurations for CVE-2019-16254

Vendor Product Version Raw CPE
ruby-lang ruby <= 2.3.0 cpe:2.3:a:ruby-lang:ruby:*:*:*:*:*:*:*:*
ruby-lang ruby >= 2.4.0, <= 2.4.7 cpe:2.3:a:ruby-lang:ruby:*:*:*:*:*:*:*:*
ruby-lang ruby >= 2.5.0, <= 2.5.6 cpe:2.3:a:ruby-lang:ruby:*:*:*:*:*:*:*:*
ruby-lang ruby >= 2.6.0, <= 2.6.4 cpe:2.3:a:ruby-lang:ruby:*:*:*:*:*:*:*:*
debian debian_linux 8.0 cpe:2.3:o:debian:debian_linux:8.0:*:*:*:*:*:*:*

References for CVE-2019-16254

URL Tags
http://lists.opensuse.org/opensuse-security-announce/2020-03/msg00041.html
https://hackerone.com/reports/331984 Third Party Advisory
https://lists.debian.org/debian-lts-announce/2019/11/msg00025.html Mailing List Third Party Advisory
https://lists.debian.org/debian-lts-announce/2019/12/msg00009.html
https://lists.debian.org/debian-lts-announce/2020/08/msg00027.html
https://lists.debian.org/debian-lts-announce/2023/04/msg00033.html
https://seclists.org/bugtraq/2019/Dec/31
https://seclists.org/bugtraq/2019/Dec/32
https://security.gentoo.org/glsa/202003-06
https://www.debian.org/security/2019/dsa-4586
https://www.debian.org/security/2019/dsa-4587
https://www.oracle.com/security-alerts/cpujan2020.html
https://www.ruby-lang.org/ja/news/2019/10/01/http-response-splitting-in-webrick-cve-2019-16254/ Vendor Advisory
https://www.ruby-lang.org/ja/news/2019/10/01/ruby-2-4-8-released/ Vendor Advisory
https://www.ruby-lang.org/ja/news/2019/10/01/ruby-2-5-7-released/ Vendor Advisory
https://www.ruby-lang.org/ja/news/2019/10/01/ruby-2-6-5-released/ Vendor Advisory
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