update to go1.26.6

[thaJeztah]

This release includes 10 security fixes following the security policy:

• x/mod/sumdb/tlog: fix transparency log tile verification bypass

  A malicious GOPROXY was previously capable of forging
  up to two sumdb tiles that allow for a requested module
  to bypass the GOSUMDB check and persist attacker-controlled
  module content to a local Go module cache.

  This attack allows for a malicious GOPROXY to serve
  malicious module content that cannot be detected
  by evaluating the transparency log.

  All tiles are now correctly verified against their parents.

  In order to determine if you have been affected:

  rm -r go.sum go.work.sum vendor/ && go mod tidy

  Thanks to Filippo Valsorda (Geomys) for reporting this issue.

  This is CVE-2026-56865 and Go issue https://go.dev/issue/80744.

• x/mod/sumdb: ignore unrelated, unauthenticated hashes in Lookup

  A malicious GOSUMDB was capable of serving arbitrary
  module content not contained within the transparency
  log.

  This attack allows for a coordinating GOPROXY and
  GOSUMDB to serve a client malicious module content
  that cannot be detected by evaluating the transparency
  log.

  In order to determine if you have been affected:

  rm -r go.sum go.work.sum vendor/ && go mod tidy

  Thanks to mundur for reporting this issue.

  This is CVE-2026-56864 and Go issue https://go.dev/issue/80745.

• encoding/xml: add recursion depth guard during decode

  Previously, DecodeElement would reset the depth counter
  causing it to never fire; this could lead to stack
  exhaustion.

  This is CVE-2026-56859 and Go issue https://go.dev/issue/80481.

net/http: apply ReadHeaderTimeout when doing unencrypted HTTP/2 check

When a server is configured to support unencrypted HTTP/2, it reads a
few bytes from each new connection to see if they contain the HTTP/2
client preface. Previously, this was being done with no timeout applied.
ReadHeaderTimeout is now applied for this.

This is CVE-2026-56853 and Go issue https://go.dev/issue/80205.

• net/url: avoid quadratic complexity in resolvePath

  Previously, resolving relative paths containing parent directory (..) segments performed string conversions and buffer rewrites on each step, resulting in quadratic time complexity and high memory allocation overhead.

  Now, path resolution operates on a byte buffer using index-based backtracking for .. segments, eliminating the quadratic time complexity and significantly reducing memory allocations.

  This is CVE-2026-56860 and Go issue https://go.dev/issue/80494.

• golang.org/x/net/dns/dnsmessage: panic when parsing invalid SVCB record

  Parsing an invalid SVCB or HTTPS RR can panic when
  the size of a parameter value overflows the message buffer.

  Thanks to Mundur (https://github.com/M0nd0R) for reporting this issue.

  This is CVE-2026-46600 and Go issue https://go.dev/issue/79795.

• crypto/tls: limit handshake messages we are willing to accept post-handshake

  Previously, we always counted handshake messages, such as KeyUpdate, as
  state-advancing, regardless of whether a handshake has been completed or
  not. As a result, a malicious client can keep sending KeyUpdate messages
  to force the server to keep performing key derivation operations
  indefinitely.

  Thanks to Qi Deng of Aurascape.ai for reporting this issue.

  This is CVE-2026-56862 and Go issue https://go.dev/issue/80528.

• html/template: fix Javascript regexp context tracking

  Previously, pathological inputs could close an
  unescaped / early, allowing for attack-controlled
  data to inject arbitrary content, potentially
  leading to XSS.

  Thanks to Ali Sherif for reporting this issue.

  This is CVE-2026-56858 and Go issue https://go.dev/issue/80435.

• x/net/idna: failure to reject ASCII-only Punycode-encoded labels

  The ToASCII and ToUnicode functions incorrectly accepted Punycode-encoded labels
  that decode to an ASCII-only label. For example, ToUnicode("xn--example-.com")
  incorrectly returned the name "example.com" rather than an error.

  The idna package implements the processing algorithm from UTS 46.
  Older versions of UTS 46 included a specification bug which permitted
  multiple ASCII labels to decode to the same Unicode label.
  UTS 46 revision 33 fixed the specification bug.
  The idna package now implements the updated specification.

  This behavior can lead to privilege escalation in programs using the idna package.
  For example, a program which performs privilege checks on the ASCII hostname
  may reject "example.com" but permit "xn--example-.com". If that program subsequently
  converts the ASCII hostname to Unicode, it will inadvertently permits access
  to the Unicode name "example.com".

  Thanks to KC1zs4 (https://github.com/KC1zs4) for reporting this issue.

  This is CVE-2026-39821 and Go issue https://go.dev/issue/78760.

• encoding/asn1: enforce maximum recursion depth

  Enforce a recursion limit in Unmarshal to prevent stack exhaustion
  when parsing deeply-nested, recursive structures.

  Thanks to Marwan Atia (marwans...@gmail.com) for reporting this issue.

  This is CVE-2026-33818 and Go issue https://go.dev/issue/80405.

- What I did

- How I did it

- How to verify it

- Human readable description for the release notes

- A picture of a cute animal (not mandatory but encouraged)

[thaJeztah]

Probably need to check if we need to cherry-pick this, or if we can use master, @vvoland

[codecov-commenter]

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