# mitmproxy v12.1.2 — mitmproxy 12.1.2

- Product: mitmproxy (https://whatsnew.fyi/product/mitmproxy)
- Vendor: mitmproxy
- Date: 2025-08-24
- Version: v12.1.2
- Original notes: https://github.com/mitmproxy/mitmproxy/releases/tag/v12.1.2
- Permalink: https://whatsnew.fyi/product/mitmproxy/releases/v12.1.2
- Labels: Platforms: Desktop

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

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- **changed** — Docker images are now built with Debian Trixie
- **fixed** — Fix mitmweb auth cookie always using the default web_port option
- **fixed** — Add missing content-length header in curl export
- **fixed** — Update log message with correct header name
- **changed** — Do not escape non-ascii characters in the JSON contentview
- **fixed** — Fix crash in mitmweb when no explicit Server-Connection is logged
- **added** — Add syntax highlighting for CSS and JavaScript contentviews
- **changed** — Display local timezone in the Timing tab of mitmweb
- **fixed** — Prevent showing the quit message in the console when no flows are available under specific configurations
- **security** — Upgrade hyper-h2 to fix a request smuggling vulnerability that affects mitmproxy's HTTP/2 to HTTP/1 translation

- Docker images are now build with Debian Trixie.
  ([#7851](https://github.com/mitmproxy/mitmproxy/pull/7851), @mhils)
- Fix mitmweb auth cookie always using the default `web_port` option.
  ([#7827](https://github.com/mitmproxy/mitmproxy/pull/7827), @sujaldev)
- fix: missing content-length header in curl export
  ([#7810](https://github.com/mitmproxy/mitmproxy/pull/7810), @mheguy)
- fix: update log message with correct header name
  ([#7802](https://github.com/mitmproxy/mitmproxy/pull/7802), @kristof-mattei)
- Update deprecated `windows-2019` runner to `windows-2025`.
  ([#7801](https://github.com/mitmproxy/mitmproxy/pull/7801), @chedieck)
- Do not escape non-ascii characters in the JSON contentview.
  ([#7740](https://github.com/mitmproxy/mitmproxy/pull/7740), @mhils)
- Fix crash in mitmweb when no explicit Server-Connection is logged.
  ([#7734](https://github.com/mitmproxy/mitmproxy/pull/7734), @lups2000)
- Add syntax highlighting for CSS and JavaScript contentviews.
  ([#7749](https://github.com/mitmproxy/mitmproxy/pull/7749), @mhils)
- Display local timezone in the Timing tab of mitmweb.
  ([#7804](https://github.com/mitmproxy/mitmproxy/pull/7804), @lups2000)
- Prevent showing the quit message in the console when no flows are available under specific configurations.
  ([#7833](https://github.com/mitmproxy/mitmproxy/pull/7833), @lups2000)

###### Security Fixes

* [GHSA-847f-9342-265h](https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h):
  Upgrade hyper-h2 to fix a request smuggling vulnerability that affects mitmproxy's
  HTTP/2 -> HTTP/1 translation. (@mhils)