CVE-2020-5249Network attack vector

Response splitting via unsanitized early-hints headers

Published Mar 2, 2020 · Updated Aug 4, 2024

HTTP response splitting in Puma before 3.12.4 and 4.0.0 through 4.3.2 allows attackers to inject headers or a response body. Puma's early-hints response path writes application-supplied header values without rejecting carriage returns, so clients treat injected text as a new header or body. Exploitation requires an application to place attacker-controlled input in an early-hints header and can enable downstream attacks such as cross-site scripting.

CVSS severity6.5
Medium
EPSS probability1.57%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP response splitting in Puma before 3.12.4 and 4.0.0 through 4.3.2 allows attackers to inject headers or a response body. Puma's early-hints response path writes application-supplied header values without rejecting carriage returns, so clients treat injected text as a new header or body. Exploitation requires an application to place attacker-controlled input in an early-hints header and can enable downstream attacks such as cross-site scripting.

The record

CVE
CVE-2020-5249
Published
Mar 2, 2020
Updated
Aug 4, 2024
Vendor
Puma
Product
Puma
Classifications
CWE-74, CWE-113
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 2, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 3.12.4
  2. Affected versionversion=>= 4.0.0, < 4.3.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Puma · Pumaversion=< 3.12.4; version=>= 4.0.0, < 4.3.3

Published CVSS scores

6.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
4.0NIST NVDAV:N/AC:L/Au:S/C:N/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
CWE-113Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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