language: count underscores in the ParseAcceptLanguage size limit

[mohammadmseet-hue]

ParseAcceptLanguage limits the number of dashes in its input to 1000 to
bound the quadratic-time cost of the tag scanner on untrusted input
(CVE-2022-32149, golang/go#56152). The scanner also treats '' as a
subtag separator, normalizing it to '-' before scanning, but the limit
counts only '-'. Input that uses '' as its separators therefore
contains no dashes and is not subject to the limit, so it can still
reach the quadratic scanner.

Count '_' as well as '-' when enforcing the limit, and add a regression
test.

Updates golang/go#56152

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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