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Message-ID: <d6f07325-e27b-4a80-8195-ea996bc7aff5@oracle.com>
Date: Fri, 8 May 2026 14:23:07 -0700
From: Alan Coopersmith <alan.coopersmith@...cle.com>
To: oss-security@...ts.openwall.com
Subject: Go 1.26.3 and Go 1.25.10 are released with 11 security
fixes
https://groups.google.com/g/golang-announce/c/qcCIEXso47M announces:
> We have just released Go versions 1.26.3 and 1.25.10, minor point releases.
>
> These releases include 11 security fixes following the security policy:
>
> * cmd/go: malicious module proxy can bypass checksum database
>
> A malicious module proxy could exploit a flaw in the go command's
> validation of module checksums to bypass checksum database validation.
>
> This vulnerability affects any user using an untrusted module proxy
> (GOMODPROXY) or checksum database (GOSUMDB).
>
> A malicious module proxy can serve altered versions of the Go toolchain.
> When selecting a different version of the Go toolchain than the
> currently installed toolchain (due to the GOTOOLCHAIN environment variable,
> or a go.work or go.mod with a toolchain line), the go command will download
> and execute a toolchain provided by the module proxy. A malicious module
> proxy can bypass checksum database validation for this downloaded
> toolchain.
>
> Since this vulnerability affects the security of toolchain downloads,
> setting GOTOOLCHAIN to a fixed version is not sufficient. You must upgrade
> your base Go toolchain.
>
> The go tool always validates the hash of a toolchain before executing it,
> so fixed versions will refuse to execute any cached, altered versions of the
> toolchain.
>
> The go tool trusts go.sum files to contain accurate hashes of the current
> module's dependencies. A malicious proxy exploiting this vulnerability to
> serve an altered module will have caused an incorrect hash to be recorded
> in the go.sum. Users who have configured a non-trusted GOPROXY can determine
> if they have been affected by running "rm go.sum ; go mod tidy ; go mod verify",
> which will revalidate all dependencies of the current module.
>
> The specific flaw in more detail:
>
> The go command consults the checksum database to validate downloaded modules,
> when a module is not listed in the go.sum file. It verifies that the module hash
> reported by the checksum database matches the hash of the downloaded module.
> If, however, the checksum database returns a successful response that contains
> no entry for the module, the go command incorrectly permitted validation to succeed.
>
> A module proxy may mirror or proxy the checksum database, in which case the go
> command will not connect to the checksum database directly. Checksums reported
> by the checksum database are cryptographically signed, so a malicious proxy
> cannot alter the reported checksum for a module. However, a proxy which returns
> an empty checksum response, or a checksum response for an unrelated module,
> could cause the go command to proceed as if a downloaded module has been validated.
>
> The go command now properly checks checksum database responses to ensure
> that the expected module signature is present, not just that if a signature is
> present it matches the expectation.
>
> Thanks to Mundur (https://github.com/M0nd0R) for reporting this issue.
>
> This is CVE-2026-42501 and Go issue https://go.dev/issue/79070.
>
> * net/http/httputil: ReverseProxy forwards queries with more than urlmaxqueryparams parameters
>
> When used with a Rewrite function, or a Director function which parses query parameters,
> ReverseProxy sanitizes the forwarded request to remove query parameters which are not
> parsed by url.ParseQuery. ReverseProxy did not take ParseQuery's limit on the total number
> of query parameters (controlled by GODEBUG=urlmaxqueryparams=N) into account.
> This could permit ReverseProxy to forward a request containing a query parameter
> that was not visible to the Rewrite function.
>
> For example, the query "a1=x&a2=x&...&a10000=x&hidden=y" could forward the parameter
> "hidden=y" while hiding it from the proxy's Rewrite function.
>
> ReverseProxy now avoids forwarding parameters that exceed the ParseQuery limit.
>
> This is CVE-2026-39825 and Go issue https://go.dev/issue/78948.
>
> * net: panic in Dial and LookupPort when handling NUL byte on Windows
>
> The Dial and LookupPort functions would panic on Windows when provided
> with an input containing a NUL (0). These functions now return an error
> rather than panicking.
>
> This is CVE-2026-39836 and Go issue https://go.dev/issue/79006.
>
> * net/mail: quadratic string concatenation in consumePhrase
>
> Pathological inputs could cause DoS through consumePhrase
> when parsing an email address according to RFC 5322.
>
> This is CVE-2026-42499 and Go issue https://go.dev/issue/78987.
>
> * net/mail: quadratic string concatentation in consumeComment
>
> Well-crafted inputs reaching ParseAddress, ParseAddressList,
> and ParseDate were able to trigger excessive CPU exhaustion
> and memory allocations.
>
> This is CVE-2026-39820 and Go issue https://go.dev/issue/78566.
>
> * cmd/go: "go bug" follows symlinks in predictable temporary filenames
>
> The "go bug" command wrote to two files with predictable names in
> the system temporary directory (for example, "/tmp").
>
> An attacker with access to the temporary directory could create a
> symlink in one of these names, causing "go bug" to overwrite the
> target of the symlink.
>
> The "go bug" command now uses os.MkdirTemp to create a safe
> working directory.
>
> Thanks to Harshit Gupta (Mr HAX) for reporting this issue.
>
> This is CVE-2026-39819 and Go issue https://go.dev/issue/78584.
>
> * cmd/go: "go tool pack" does not sanitize output paths
>
> The "go tool pack" subcommand is a minimal version of the Unix ar utility.
> It is used by the compiler as an internal tool with known-good inputs.
>
> The "pack" subcommand did not sanitize output filenames.
> When invoked to extract a malicious archive file, it could write
> files to arbitrary locations on the filesystem.
>
> The "pack" subcommand now refuses to extract files with names
> containing any directory components.
>
> Thanks to Harshit Gupta (Mr HAX) for reporting this issue.
>
> This is CVE-2026-39817 and Go issue https://go.dev/issue/78778.
>
> * net/http: infinite loop in HTTP/2 transport when given bad SETTINGS_MAX_FRAME_SIZE
>
> When processing HTTP/2 SETTINGS frames, transport will enter an infinite loop of
> writing CONTINUATION frames if it receives a SETTINGS_MAX_FRAME_SIZE with a
> value of 0.
>
> This allows potential DoS against a client by a malicious server. HTTP/2
> transport now properly checks that the received SETTINGS_MAX_FRAME_SIZE is
> valid.
>
> Thanks to Marwan Atia (marwans...@...il.com) for reporting this issue.
>
> This is CVE-2026-33814 and Go issue https://go.dev/issue/78476.
>
> * html/template: escaper bypass leads to XSS
>
> If a trusted template author were to write a
> tag containing an empty type attribute or a type
> attribute with an ASCII whitespace, the execution of
> the template would incorrectly escape any data passed
> into the block.
>
> Thanks to Mundur (https://github.com/M0nd0R) for reporting this issue.
>
> This is CVE-2026-39826 and Go issue https://go.dev/issue/78981.
>
> * net: crash when handling long CNAME response
>
> When using LookupCNAME with the cgo DNS resolver,
> a very long CNAME response could trigger a double-free of C memory
> and a crash. The double-free has been fixed.
>
> Thanks to hamayanhamayan for reporting this issue.
>
> This is CVE-2026-33811 and Go issue https://go.dev/issue/78803.
>
> * html/template: bypass of meta content URL escaping causes XSS
>
> CVE-2026-27142 fixed a vulnerability in which URLs were not
> correctly escaped inside of a tag's attribute.
> If the URL content were to insert ASCII whitespaces around the
> = rune inside of the attribute, the escaper would
> fail to similarly escape it, leading to XSS.
>
> Dynamic inputs to a tag's attribute are now
> whitespace sanitized prior to escaping.
>
> Thanks to Samy Ghannad for reporting this issue.
>
> This is CVE-2026-39823 and Go issue https://go.dev/issue/78913.
>
> View the release notes for more information:
> https://go.dev/doc/devel/release#go1.26.3
>
> 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 go1.26.3 and build as usual.
>
> Thanks to everyone who contributed to the releases.
>
> Cheers,
> Cherry and Michael for the Go team
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