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                            CERT-Renater

                Note d'Information No. 2026/VULN581
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DATE                : 03/06/2026

HARDWARE PLATFORM(S): /

OPERATING SYSTEM(S): Systems running Go versions prior to 1.26.4,
                                        1.25.11.

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https://groups.google.com/g/golang-announce/c/tKs3rmcBcKw/m/1ou-Xt7gAQAJ
_____________________________________________________________________

Hello gophers,

We have just released Go versions 1.26.4 and 1.25.11, minor point releases.

These releases include 3 security fixes following the security policy:

    mime: quadratic complexity in WordDecoder.DecodeHeader

    Decoding a maliciously-crafted MIME header containing many invalid
    encoded-words could consume excessive CPU.
    The MIME decoder now better handles this case.

    Thanks to p4p3r (https://hackerone.com/p4p3r_hak) for reporting this issue.

    This is CVE-2026-42504 and Go issue https://go.dev/issue/79217.

    net/textproto: arbitrary input are included in errors without any escaping

    When returning errors, functions in the net/textproto package would
    include its input as part of the error, without any escaping. Note that
    said input is often controlled by external parties when using this
    package naturally. For example, a net/http client uses ReadMIMEHeader
    when parsing the headers it receive from a server.

    As a result, an attacker could inject arbitrary content into the error.
    Practically, this can result in an attacker injecting misleading
    content, terminal control bytes, etc. into a victim's output or logs.

    This is CVE-2026-42507 and Go issue https://go.dev/issue/79346

    crypto/x509: split candidate hostname only once

    (*x509.Certificate).VerifyHostname previously called matchHostnames in a loop
    over all DNS Subject Alternative Name (SAN) entries. This caused
    strings.Split(host, ".") to execute repeatedly on the same input hostname.

    With a large DNS SAN list, verification costs scaled quadratically based on the
    number of SAN entries multiplied by the hostname's label count. Because
    x509.Verify validates hostnames before building the certificate chain, this
    overhead occurred even for untrusted certificates.

    Thanks to Jakub Ciolek (https://ciolek.dev) for reporting this issue.

    This is CVE-2026-27145 and https://go.dev/issue/79694.

View the release notes for more information:
https://go.dev/doc/devel/release#go1.26.4

You can download binary and source distributions from the Go website:
https://go.dev/dl/

To compile from source using a Git clone, update to the release with
git checkout go1.26.4 and build as usual.

Thanks to everyone who contributed to the releases.

Cheers,
The Go team

=========================================================
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+ 23/25 Rue Daviel    |    fax : 01-53-94-20-41         +
+ 75013 Paris         |   email:cert@support.renater.fr +
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