Log Message:
go121: update to 1.21.5 (security)

This minor release includes 3 security fixes following the security policy:

- net/http: limit chunked data overhead

  A malicious HTTP sender can use chunk extensions to cause a receiver reading
  from a request or response body to read many more bytes from the network than
  are in the body.

  A malicious HTTP client can further exploit this to cause a server to
  automatically read a large amount of data (up to about 1GiB) when a handler
  fails to read the entire body of a request.

  Chunk extensions are a little-used HTTP feature which permit including
  additional metadata in a request or response body sent using the chunked
  encoding. The net/http chunked encoding reader discards this metadata. A
  sender can exploit this by inserting a large metadata segment with each byte
  transferred. The chunk reader now produces an error if the ratio of real body
  to encoded bytes grows too small.

  Thanks to Bartek Nowotarski for reporting this issue.
  This is CVE-2023-39326 and Go issue https://go.dev/issue/64433.

- cmd/go: go get may unexpectedly fallback to insecure git

  Using go get to fetch a module with the ".git" suffix may unexpectedly
  fallback to the insecure "git://" protocol if the module is \ 
unavailable via
  the secure "https://" and "git+ssh://" protocols, even if \ 
GOINSECURE is not
  set for said module. This only affects users who are not using the module
  proxy and are fetching modules directly (i.e. GOPROXY=off).

  Thanks to David Leadbeater for reporting this issue.
  This is CVE-2023-45285 and Go issue https://go.dev/issue/63845.

- path/filepath: retain trailing \ when cleaning paths like \\?\c:\

  Go 1.20.11 and Go 1.21.4 inadvertently changed the definition of the volume
  name in Windows paths starting with \\?\, resulting in
  filepath.Clean(\\?\c:\) returning \\?\c: rather than \\?\c:\ (among other
  effects). The previous behavior has been restored.

  This is an update to CVE-2023-45283 and Go issue https://go.dev/issue/64028.