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Fencer Vulns
medium 6.5

CVE-2020-5249 json

HTTP Response Splitting (Early Hints) in Puma

published 2020-03-02 6 y ago modified 2026-06-17 4 mo ago also GHSA-33vf-4xgg-9r58 , EUVD-2020-0325

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.6%
EPSS 1.6% chance of exploitation in 30 days, percentile 75%
public exploits
0
none known

Summary

In Puma (RubyGem) before 4.3.3 and 3.12.4, if an application using Puma allows untrusted input in an early-hints header, an attacker can use a carriage return character to end the header and inject malicious content, such as additional headers or an entirely new response body. This vulnerability is known as HTTP Response Splitting. While not an attack in itself, response splitting is a vector for several other attacks, such as cross-site scripting (XSS). This is related to CVE-2020-5247, which fixed this vulnerability but only for regular responses. This has been fixed in 4.3.3 and 3.12.4.

Patch / fix

  • rubygems puma 3.12.4, 4.3.3
  • puma Debian 14, Debian 13, Debian 12 3.12.4-1

debian advisories DEBIAN-CVE-2020-5249

  • rmt-server SLE Module for Server Applications 15 SP1, SLE Module for Public Cloud 15 SP1 2.6.5-3.18.1
  • rmt-server SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 2.6.5-3.34.1
  • rmt-server SLE Module for Server Applications 15 SP2, SLE Module for Public Cloud 15 SP2 2.6.5-3.3.1

suse advisories SUSE-SU-2020:3160-1SUSE-SU-2020:3147-1SUSE-SU-2020:3036-1

  • rmt-server openSUSE Leap 15.1 2.6.5-lp151.2.18.2
  • rmt-server openSUSE Leap 15.2 2.6.5-lp152.2.3.1

opensuse advisories openSUSE-SU-2020:2000-1openSUSE-SU-2020:1993-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2020-5249 updated cvss 0.0

rubygem-puma: attacker is able to use carriage return character to insert malicious content (HTTP Response Splitting), this could lead to XSS

  • Red Hat CloudForms Management Engine 5 rubygem-puma Red Hat Software Collections rh-ror50-rubygem-puma Red Hat Storage 3 rubygem-puma
    affected: no fix planned “Will not fix”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.57% chance of exploitation in the next 30 days, higher than 75% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
NVD 2.0 4.0 AV:N/AC:L/Au:S/C:N/I:P/A:N
GitHub 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L

Affected packages

ecosystem package affected fixed in
rubygems puma
<3.12.4
>=4.0.0, <4.3.3
3.12.4
4.3.3

Affected products

  • puma Puma

Classification

Weakness
  • CWE-113 Improper Neutralization of CRLF Sequences in HTTP Headers
  • CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.