net/mail: excessive CPU consumption in ParseAddress (CVE-2025-61725)

[neild]

The ParseAddress function constructed domain-literal address components through repeated string concatenation. When parsing large domain-literal components, this could cause excessive CPU consumption.

Thanks to Philippe Antoine (Catena cyber) for reporting this issue.

This is CVE-2025-61725 and Go issue https://go.dev/issue/75680.

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This is a PRIVATE issue for CVE-2025-61725, tracked in http://b/446728192 and fixed by https://go-internal-review.git.corp.google.com/c/go/+/2840.

/cc @golang/security and @golang/release

[neild]

@gopherbot please open backport issues for this security fix

[gopherbot]

Backport issue(s) opened: #75700 (for 1.24), #75701 (for 1.25).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.

[gopherbot]

Change https://go.dev/cl/709835 mentions this issue: [release-branch.go1.24] net/mail: avoid quadratic behavior in mail address parsing

[gopherbot]

Change https://go.dev/cl/709860 mentions this issue: net/mail: avoid quadratic behavior in mail address parsing

[gopherbot]

Change https://go.dev/cl/709844 mentions this issue: [release-branch.go1.25] net/mail: avoid quadratic behavior in mail address parsing