CVE-2026-42874 Microdot: HTTP response splitting in Response.set_cookie()
Microdot allows HTTP response splitting via unsanitized cookie values, enabling header injection if an attacker controls client-side input.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42874?
CVE-2026-42874 is a low-severity vulnerability in miguelgrinberg microdot, published on 11 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-113
Which versions are affected by CVE-2026-42874?
3 open source packages ship an affected version, including microdot.
| Package | Affected | Fixed in |
|---|---|---|
microdot PyPI | All versions | 2.6.1 |
microdot PyPI | All versions | 2.6.1 |
microdot PyPI | All versions | 2.6.1 |
How do I fix CVE-2026-42874?
Upgrade microdot to 2.6.1 or later.
Is CVE-2026-42874 being exploited?
There is no known exploitation of CVE-2026-42874 in the wild and no public exploit code.
Sources
Also known as GHSA-7wc8-wvc4-m498, PYSEC-2026-2646.