CVE-2026-42874Network attack vector

Response-header injection via unsanitized cookie strings

Published May 11, 2026 · Updated May 11, 2026

HTTP response splitting in Microdot before 2.6.1 allows context-dependent attackers to inject response headers through cookie data. Response.set_cookie() concatenates untrusted cookie, value, path, and domain strings into a Set-Cookie header without rejecting carriage returns or line feeds. Reachability requires an already infiltrated client and application code that stores its supplied data in a cookie; injected headers affect only responses to that client.

CVSS severity3.7
Low
EPSS probability0.21%
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 Microdot before 2.6.1 allows context-dependent attackers to inject response headers through cookie data. Response.set_cookie() concatenates untrusted cookie, value, path, and domain strings into a Set-Cookie header without rejecting carriage returns or line feeds. Reachability requires an already infiltrated client and application code that stores its supplied data in a cookie; injected headers affect only responses to that client.

The record

CVE
CVE-2026-42874
Published
May 11, 2026
Updated
May 11, 2026
Vendor
Miguel Grinberg
Product
Microdot
Classifications
CWE-113
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 11, 2026CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record 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=< 2.6.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Miguel Grinberg · Microdotversion=< 2.6.1

Published CVSS scores

3.7GitHubCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-113Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')

Public exploit references

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Technologies

Your stack

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Your stack

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