Go 1.27.4 and Go 1.26.11 are released with 12 security fixes

[Alan Coopersmith <alan.coopersmith () oracle com>]

-------- Forwarded Message --------
Subject:        [security] Go 1.27.4 and Go 1.26.11 are released
Date:   Tue, 10 Nov 2026 17:14:54 +0000
From:   announce () golang org
To:     golang-nuts () googlegroups com

Hello gophers,

We have just released Go versions 1.27.4 and 1.26.11, minor point releases.

These releases include 12 security fixes following the security policy <https://go.dev/doc/security/policy>:

  * net/http: HTTP/1 server crash due to MaxBytesReader header race

    For HTTP/1 servers, when MaxBytesReader's limit is exceeded,
    "Connection: close" header is automatically set without synchronization,
    which might race with another header being set explicitly in the server
    handler. As a result, an HTTP/1 server that utilizes MaxBytesReader or
    MaxBytesHandler can crash due to runtime panic if its handler reads the
    request body concurrently with writing the response header.

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

    This is CVE-2026-97054 and Go issue <https://go.dev/issue/82563>.

  * cmd/go: unexpected code execution via --sysroot, -target, -isysroot,
    -Wl,-syslibroot, and -x cgo flags

    Building a malicious package that uses cgo could cause arbitrary code execution
    at build time through several compiler and linker flags permitted in "#cgo"
    directives.

    Specifically, "--sysroot" in GCC and Clang relocates compiler subprograms, spec
    files, and CRT startup objects to an attacker-controlled directory; "-target" in
    Clang falls back to executing target helper tools from the current working
    directory when not found in PATH; "-isysroot" and "-Wl,-syslibroot" can pass a
    regular file on disk to GNU ld.bfd, which interprets it as a positional linker
    script; and "-x" permitted specifying arbitrary compiler input languages beyond
    those supported by cgo.

    "--sysroot" and "-target" are now disallowed in "#cgo" flags, "-isysroot" and
    "-Wl,-syslibroot" are verified not to point to regular files, and "-x" is
    restricted to the C, C++, Objective-C, and assembler languages supported by cgo.

    This issue was found by the Go Security Team during an internal audit.

    This is CVE-2026-97033 and Go issue <https://go.dev/issue/82577>.

  * cmd/go: arbitrary command execution via GCC spec files in cgo linker search
    directories

    When using GCC, building a malicious package that uses cgo could cause arbitrary
    command execution at link time via untrusted GCC spec files ("specs" or
    "*.spec").

    When linking with "-fopenmp", "-fopenacc", or "-fsanitize=" in "#cgo LDFLAGS",
    GCC's built-in link spec evaluates "%:include(libgomp.spec)" or
    "%:include(libsanitizer.spec)" and searches for spec files in "-L" and sysroot
    directories (including subdirectories and multilib sibling directories such as
    "../lib64"), as well as the working directory when "-fopenmp" or "-fopenacc" is
    used or when "-fsanitize=" is combined with "-static" or "-static-lib*".

    The go command now rejects "-L", "-isysroot", and "-Wl,-syslibroot" directories
    (and the working and package directories when applicable) that contain GCC spec
    files, and disallows "@" and "-" prefixes in "-fsanitize=" compiler flag values.

    This issue was found by the Go Security Team during an internal audit.

    This is CVE-2026-97034 and Go issue <https://go.dev/issue/82576>.

  * cmd/go: unexpected code execution and arbitrary file write via Clang -gen-*
    and GCC -gnat* flags in cgo

    When using Clang or GCC, building a malicious package that uses cgo could cause
    unexpected code execution at build time or write files to arbitrary
    directories via "-gen-/" or "-gnat/" flags in "#cgo" directives.

    The "-g*" wildcard in the compiler and linker flag allowlists previously
    matched Clang's two-argument "-gen-cdb-fragment-path " flag and GCC's
    two-argument "-gnatO " flag, permitting compilation database fragments
    and sidecar output files to be written to arbitrary directories and
    desynchronizing flag argument parsing between the go command and the compiler
    driver so that subsequent arguments could be passed as unvalidated positional
    inputs to the linker.

    "-gen-/" and "-gnat/" flags are now disallowed in "#cgo" compiler and linker
    flags.

    This issue was found by the Go Security Team during an internal audit.

    This is CVE-2026-97035 and Go issue <https://go.dev/issue/82575>.

  * cmd/go: arbitrary code execution during build on darwin via "-l to_library"
    in cgo

    On Darwin, building a malicious package that uses cgo could cause arbitrary code
    execution when using the Apple linker due to passing "-l to_library " in a
    "#cgo LDFLAGS" directive.

    The Apple linker recombines the separated arguments "-l" and "to_library" into
    "-lto_library", which loads an arbitrary LTO plugin dynamic library at link
    time.

    The go command now disallows "-l" followed by "to_library" in "#cgo LDFLAGS",
    rejects "-lazy_library", "-lazy_framework", "-load_hidden", "-library", and
    "-library-path", and checks recombined "-l" arguments against disallowed linker
    flags and patterns.

    Thanks to Ali Sherif (<https://www.linkedin.com/in/ali-sherif-13812b276/>) for
    reporting this issue.

    This is CVE-2026-97036 and Go issue <https://go.dev/issue/82574>.

  * cmd/go: linker script injection via split -Wl, flags and Darwin or symbol
    linker flags in cgo

    Building a malicious package that uses cgo could cause arbitrary code execution
    at link time by passing linker script files to the host linker via "#cgo
    LDFLAGS".

    Split "-Wl," flags that consume a following argument (such as "-Wl,-rpath",
    "-Wl,--just-symbols", and "-Wl,-undefined") previously accepted a bare second
    argument without a "-Wl," prefix, which the compiler driver passes directly to
    the linker as a positional input file. Additionally, when using GNU ld.bfd,
    flags such as "-framework", "-Wl,-framework", "-Wl,-undefined",
    "-Wl,--just-symbols", "-Wl,-R", "-Wl,-subsystem", and (on non-Darwin platforms)
    "-Wl,-sectcreate" could cause ld.bfd to interpret their arguments as linker
    scripts if they named a regular file on disk.

    The go command now requires a "-Wl," prefix on the second token of split "-Wl,"
    flags (except "-Wl,-R"), verifies that these flags do not reference linker
    script files, and disallows bare "-Wl,--warn-backrefs-exclude".

    This issue was found by the Go Security Team during an internal audit.

    This is CVE-2026-97037 and Go issue <https://go.dev/issue/82573>.

  * cmd/go: arbitrary code execution via crafted .syso files and cgo linker
    input files

    Building a malicious package containing ".syso" files or cgo linker inputs could
    inject arbitrary linker flags or execute arbitrary code at link time.

    Linker input files—including ".syso" files, direct object or library inputs in
    "#cgo LDFLAGS", and libraries in "-L" directories—were passed to the external
    linker without validating their format or checking for embedded linker options.
    Across platforms, this allowed executing GNU ld implicit linker scripts
    disguised as libraries or ".syso" files (or loaded via "-l:" or "-l"
    containing path separators), injecting unallowlisted linker flags via PE/COFF
    ".drectve" sections on Windows or Mach-O "LC_LINKER_OPTION" load commands on
    Darwin, or invoking LTO plugins via GCC or LLVM LTO intermediate representation
    sections in ELF, PE/COFF, or Mach-O objects.

    The go command now verifies that ".syso" files, direct linker inputs, and
    libraries in "-L" directories are valid binary objects or archives that do not
    contain unallowlisted ".drectve" directives, "LC_LINKER_OPTION" load commands,
    or LTO IR sections, and disallows "-l:" and ":", "=", or path
    separators in "-l" flags.

    This issue was found by the Go Security Team during an internal audit.

    This is CVE-2026-97038 and Go issue <https://go.dev/issue/82572>.

  * cmd/go: flag sanitization bypass via "#cgo pkg-config:" directives

    Building a malicious package that uses "#cgo pkg-config:" directives could
    load untrusted pkg-config ".pc" files or inject unvalidated compiler and linker
    flags.

    The pkg-config flag allowlist previously permitted "--with-path=" and
    "--personality=", allowed "--define-variable=" values beginning with "=" or "$"
    (which can rewrite paths in system ".pc" files into sysroot-prefixed "-L=" or
    "-L$SYSROOT" linker search paths), and allowed package arguments ending in ".pc"
    or containing path separators or "..", which caused pkg-config to load local
    ".pc" files directly from the package directory. In addition, flags returned by
    "pkg-config --cflags" in cgoCPPFLAGS were not checked when determining whether
    internal linking is safe.

    The go command now disallows "--with-path=", "--personality=", leading "=" or
    "$" characters in "--define-variable=" values, and local ".pc" paths in
    "#cgo pkg-config:" directives, and inspects cgoCPPFLAGS when checking internal
    linking compatibility.

    This issue was found by the Go Security Team during an internal audit.

    This is CVE-2026-97039 and Go issue <https://go.dev/issue/82571>.

  * cmd/go, cmd/link: cgo directive injection via .syso files disguised as Go
    object files

    Building a package containing a crafted ".syso" file could bypass cgo flag
    validation and inject arbitrary linker flags when linking.

    When loading ".syso" entries from a package archive, the linker only checked for
    recognized host object headers (ELF, Mach-O, PE, and XCOFF) before falling
    through to Go object parsing. A ".syso" file beginning with a "go object" header
    was parsed as a Go compiler object, allowing untrusted cgo metadata directives
    (such as "cgo_ldflag" or "cgo_dynamic_linker") embedded in the ".syso" file to
    be passed to the external linker without validation. Additionally, ".syso"
    filenames longer than 16 bytes lost their ".syso" extension when truncated in
    archive headers, and unrecognized ".syso" formats forced external linking in
    pure-Go builds.

    The linker now rejects ".syso" files that are not recognized host object
    formats, and "cmd/go" and "cmd/pack" preserve the ".syso" suffix when truncating
    long archive member names.

    Thanks to RyotaK (<https://ryotak.net>) of GMO Flatt Security Inc. for reporting
    this issue.

    This is CVE-2026-97040 and Go issue <https://go.dev/issue/82570>.

  * cmd/compile, cmd/link: host linker flag injection via //go:cgo_* directives

    Building a malicious package containing "//go:cgo_*" compiler directives could
    inject arbitrary flags into the external linker invocation on ELF platforms.

    The compiler and linker did not reject commas in "//go:cgo_import_dynamic",
    "//go:cgo_export_dynamic", "//go:cgo_export_static", "//go:cgo_import_static",
    and "//go:cgo_dynamic_linker" directives, and the linker passed the dynamic
    linker path using "-Wl,--dynamic-linker,". Furthermore, the two-argument
    form of "//go:cgo_import_dynamic" (which is permitted in non-cgo Go source
    files) could overwrite the external symbol name of a symbol already marked for
    cgo export. A symbol name or dynamic linker path containing a comma or leading
    "@" could split "-Wl,--export-dynamic-symbol=" or "-Wl,--dynamic-linker," into
    arbitrary host linker flags or response file arguments.

    The compiler and linker now reject commas in "//go:cgo_*" symbol and dynamic
    linker directives, the linker passes "-Wl,--dynamic-linker=", and
    "cgo_import_dynamic" no longer overwrites symbols exported via
    "cgo_export_dynamic" or "cgo_export_static".

    Thanks to RyotaK (<https://ryotak.net>) of GMO Flatt Security Inc. for reporting
    this issue.

    This is CVE-2026-97041 and Go issue <https://go.dev/issue/82569>.

  * cmd/cgo, cmd/compile, cmd/link: linker flag injection via cgo_import_dynamic
    and PE DLL names

    Building a malicious package that uses "//go:cgo_import_dynamic" or links
    against a crafted PE object on Windows could pass unsafe library arguments to
    the external linker.

    The compiler only checked the first character of the library name in
    "//go:cgo_import_dynamic" directives and skipped validation in cgo-generated
    files. In addition, on Windows, "cmd/cgo" and "cmd/link" did not validate
    imported DLL names extracted from PE object files before emitting "-l"
    flags for the external linker, allowing a crafted DLL name containing ".." path
    traversal or special characters to reference arbitrary files on disk.

    The compiler now validates every character of the library name in
    "//go:cgo_import_dynamic" directives (including in cgo-generated files on
    Windows) and rejects ".." path traversal, and "cmd/cgo" and "cmd/link" reject
    PE imported DLL names containing path separators, "..", ":", or leading "-" or
    "@".

    This issue was found by the Go Security Team during an internal audit.

    This is CVE-2026-97042 and Go issue <https://go.dev/issue/82568>.

  * cmd/go, cmd/compile: unexpected code execution via escaped quotes in
    //go:cgo_ldflag

    Building a malicious package that uses cgo could bypass "#cgo LDFLAGS"
    validation and cause unexpected code execution at build time, or cause the go
    command to panic, via crafted quoting in "//go:cgo_ldflag" directives.

    When "cmd/cgo" generates "_cgo_gotypes.go", it quotes each "#cgo LDFLAGS"
    argument with strconv.Quote in a "//go:cgo_ldflag" directive, but "cmd/compile"
    and "cmd/go" parsed those directives by splitting on raw quote characters
    without handling backslash escapes or unquoting the string. This mismatch
    allowed disallowed linker flags or unvalidated linker search paths to be
    smuggled past the go command's flag checks and passed to the external linker.
    In addition, deduplicating LDFLAGS in the go command could panic with an
    out-of-bounds slice index when a prefix of the flag list matched near the end
    of the slice.

    "cmd/compile" and "cmd/go" now properly handle backslash-escaped quotes and
    unquote "//go:cgo_*" pragma strings with strconv.Unquote, and the slice bounds
    check in processCgoOutputs has been fixed.

    This issue was found by the Go Security Team during an internal audit.

    This is CVE-2026-97043 and Go issue <https://go.dev/issue/82567>.

View the release notes for more information:
https://go.dev/doc/devel/release#go1.27.4

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 go1.27.4| and build as usual.

Thanks to everyone who contributed to the releases.

Cheers,
Cherry and Junyang for the Go team

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