What’s Vulnerable › Vulnerabilities

CVE-2026-42874: Microdot: HTTP response splitting in Response.set_cookie()

• Severity: low (CVSS 3.7 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-11 · updated 2026-10-26
• Weakness: CWE-113

Description

Microdot is a minimalistic Python web framework. Prior to 2.6.1, the Response.set_cookie() method does not sanitize its string arguments, and in particular will not detect the presence of the \r\n sequence in them. This can be a potential source of header injection attacks. For a header injection attack through this issue to be possible, an attacker must first infiltrate the client (for example through an independent XSS attack), so that it can send malicious information that is destined to be stored in a cookie by the server on behalf of the victim. An attacker that infiltrates one client can only orchestrate a header injection attack for that client, all other clients that were not infiltrated are safe. This vulnerability is fixed in 2.6.1.

Affected products

• miguelgrinberg microdot: before 2.6.1

References

• https://github.com/miguelgrinberg/microdot/blob/main/CHANGES.md
• https://github.com/miguelgrinberg/microdot/commit/99b281b45faef8472410f2d56bfef496dfbd95d5
• https://github.com/miguelgrinberg/microdot/security/advisories/GHSA-7wc8-wvc4-m498

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