GHSA-mqxv-9rm6-w8qc Ech0: ParseAcceptLanguage `_` separator bypass enables ~70x CPU amplification via Accept-Language header in i18n.Middleware
SummaryEch0's i18n middleware runs on every HTTP request and constructs a fresh `*goi18n.Localizer` from the raw `Accept-Language` header without imposing any size or shape filter. `goi18n.NewLocalizer` calls `golang.org/x/text/language.ParseAcceptLanguage` on the value internally. The underlying parser has quadratic-time behaviour on long lists of malformed language tags. The CVE-2022-32149 guard that golang.org/x/text added in v0.3.8 caps the number of `-` characters in the input at 1000, but it does not cap `_` characters even though the parser's internal scanner aliases `_` to `-` before parsing. A single unauthenticated GET request with an `Accept-Language` header built out of `_` separators burns about 1.5 seconds of server CPU on the host running Ech0; ten concurrent attackers saturate a ten-core box for the duration of the attack while consuming ~10 MiB/s of upstream bandwidth.Affected versions`github.com/lin-snow/Ech0` v4.8.2 and (per code inspection of `main`) earlier 4.x versions that wire the `internal/i18n.Middleware()` gin middleware on the global router without imposing their own size limit on `Accept-Language`. Verified on:the official `ghcr.io/lin-snow/ech0:latest` Docker image at v4.8.2 (E2E below)`main` at commit `451c7c10eb1f23f7525c163e83f8b39f46d5aad0` by reading `internal/i18n/i18n.go` (the middleware and `setLocaleContext` call site are unchanged)Privilege requiredUnauthenticated. The `i18n.Middleware` runs for every HTTP request including the public landing page, the public comments feed, and the unauthenticated `/api/echo/page` endpoint.Vulnerable code[`internal/i18n/i18n.go`](https://github.com/lin-snow/Ech0/blob/451c7c10eb1f23f7525c163e83f8b39f46d5aad0/internal/i18n/i18n.go) (blob SHA `451c7c10eb1f23f7525c163e83f8b39f46d5aad0`), the gin middleware `Middleware()` at lines 202-213:`setLocaleContext` at line 191 then calls `NewLocalizer(normalized, acceptLanguage)`:`NewLocalizer` is a thin wrapper around `goi18n.NewLocalizer`, which internally calls `language.ParseAcceptLanguage(lang)` for every passed string in its `parseTags` helper (see `github.com/nicksnyder/go-i18n/v2@v2.6.0/i18n/localizer.go:42-50`). So the unfiltered `acceptLanguage` reaches `language.ParseAcceptLanguage` on every request.`ctx.GetHeader("Accept-Language")` is the unfiltered HTTP header. Go's default `net/http` `MaxHeaderBytes` is `1 << 20` = 1 MiB and Ech0 does not override it, so the parser is allowed to receive up to a megabyte of attacker-controlled data.The additional `ResolveLocale` path at line 208 also calls `language.ParseAcceptLanguage(strings.Join(parts, ","))` directly when `X-Locale` or the `lang` query parameter is set, with the same vector and a longer-running effect (the input concatenates `explicit + acceptLanguage` so the parser sees both, and the path is exercised twice).CVE-2022-32149 hardened `ParseAcceptLanguage` by counting `-` characters and rejecting inputs with more than 1000 of them. The guard does not count `_` characters even though the scanner converts `_` to `-` at parse time ([`golang.org/x/text/internal/language/parse.go`](https://github.com/golang/text/blob/v0.28.0/internal/language/parse.go)). A 1 MiB header full of 9-character `_abcdefghi` tokens contains zero `-` characters, passes the guard, and then drives the scanner into the O(N²) `gobble` path.How `Accept-Language` reaches `ParseAcceptLanguage`The middleware sequence on any HTTP request:The request enters `i18n.Middleware()`.`ctx.GetHeader("Accept-Language")` returns the full attacker-supplied header value.`setLocaleContext` is called with that value.`NewLocalizer(normalized, acceptLanguage)` constructs a goi18n localizer; goi18n's `parseTags` calls `language.ParseAcceptLanguage(acceptLanguage)` unfiltered.No size or character-class filter is applied between (2) and (4). When `X-Locale` or `?lang=` is also present, the parser is invoked twice on related input via the explicit `ResolveLocale(explicit, acceptLanguage)` path at line 210.Proof of conceptSingle-line bash reproducer that crafts the malicious header and times one request against a fresh `ghcr.io/lin-snow/ech0:latest` container:Each 9-character `_abcdefghi` token has length 9, which fails the scanner's `len <= 8` tag-length check at `golang.org/x/text/internal/language/parse.go` and triggers a `gobble` call that `runtime.memmove`s the entire remaining buffer. With N invalid tokens the total bytes moved by `gobble` is O(N²).End-to-end reproduction (against `ghcr.io/lin-snow/ech0:latest` at v4.8.2)A Go driver `poc.go` boots the container, sends a 1 MiB `Accept-Language` value once with `-` (CVE-2022-32149 guard fires) and once with `_` (guard bypassed):Captured run output (Apple M1 Pro, darwin/arm64, Go 1.26.1, the official `ghcr.io/lin-snow/ech0:latest` image at v4.8.2):Setting `X-Locale: en` in addition (which triggers the explicit-locale `ResolveLocale` path at line 210, calling `ParseAcceptLanguage(strings.Join(parts, ","))` directly) makes the same request take ~7.9 s on the same host — the attacker doubles the work by adding one short header. Setting `?lang=en` in the query gives ~3 s.Interpretation:| Request                                  | Header bytes | Server time |
|------------------------------------------|--------------|-------------|
| no header / short tag                    | 0 - 5        | 2 - 8 ms    |
| 1 MiB `-` separators (CVE-2022-32149 guard fires) | 1 MiB | 21 ms       |
| 1 MiB `_` separators (guard bypassed), no X-Locale | 1 MiB | 1.5 - 1.6 s |
| 1 MiB `_` separators with X-Locale: en   | 1 MiB        | ~7.9 s      |The `-` control proves that the existing CVE-2022-32149 guard does still work on the canonical separator. The `_` attack returns 200 from the same endpoint but consumes ~1.5 s of server CPU on the default path and ~7.9 s when the attacker adds a one-byte `X-Locale: en` header. The amplification factor at the application boundary is ~70x in the default case (21 ms guard-fires vs 1.5 s attack on the same 1 MiB header) and ~370x in the X-Locale variant.ImpactOne unauthenticated client can pin one CPU core for ~1.5 seconds per 1 MiB request, or ~7.9 seconds if the attacker adds the `X-Locale: en` header.Ten concurrent attackers using ~10 MiB/s of upstream bandwidth pin a 10-core Ech0 instance indefinitely.The endpoint returns 200 OK, so the attack does not surface as abnormal traffic in standard 4xx/5xx dashboards.Self-hosted Ech0 instances published to the public internet (the documented use case) are exposed.Suggested fixApply the size / character-class filter at the i18n middleware boundary, before the `Accept-Language` value reaches `setLocaleContext` (and through it `NewLocalizer`). The smallest change that preserves the existing behaviour for legitimate Accept-Language headers is to count `_` alongside `-` and drop the header when the total exceeds a small ceiling:The same `sanitizeAcceptLanguage` should be applied wherever `Accept-Language` is consumed (`HeaderLocale` at line 230 and the `user.go` paths at lines 80, 275 that pass user input into `ResolveLocale`).A real Accept-Language header from a browser contains under 10 separators, so a ceiling of 32 leaves plenty of headroom while making the quadratic blow-up impossible.The underlying issue is in `golang.org/x/text/language`. A future upstream fix is the right long-term solution; the change above is defensive-in-depth at the middleware that consumes attacker input.CreditReported by tonghuaroot.Fix PRhttps://github.com/lin-snow/Ech0-ghsa-mqxv-9rm6-w8qc/pull/1
CVSS v4.0 score: 8.7