Overview
The Ech0 ParseAcceptLanguage vulnerability is a critical issue affecting the Ech0 application, specifically its i18n middleware. This vulnerability allows an unauthenticated attacker to cause a significant amplification of CPU consumption via a specially crafted Accept-Language header. The vulnerability has a CVSS score of 8.7, indicating a high severity level.
Understanding the Vulnerability / Threat
Root Cause Analysis
The root cause of this vulnerability lies in the i18n middleware of the Ech0 application. The middleware is responsible for constructing a fresh `*goi18n.Localizer` from the raw `Accept-Language` header without imposing any size or shape filter. The `goi18n.NewLocalizer` function calls `golang.org/x/text/language.ParseAcceptLanguage` internally, which has quadratic-time behavior on long lists of malformed language tags.
The CVE-2022-32149 guard added in `golang.org/x/text` version 0.3.8 caps the number of `-` characters in the input at 1000 but does not cap `_` characters. The parser's internal scanner aliases `_` to `-` before parsing, allowing an attacker to bypass the guard by using `_` characters.
This vulnerability belongs to the CWE category of 'Improper Input Validation'.
Attack Surface & Vector
The attack surface of this vulnerability is the i18n middleware, which runs on every HTTP request, including public landing pages, comments feeds, and unauthenticated endpoints. An attacker can reach this vulnerability by sending a specially crafted Accept-Language header in an HTTP request.
The preconditions needed for this vulnerability to be exploited are:
- The Ech0 application is running a vulnerable version (v4.8.2 or earlier 4.x versions).
- The i18n middleware is wired on the global router without imposing a size limit on the Accept-Language header.
Exploitation Mechanics — Scenario Walkthrough
Scenario: Compromising a Corporate Ech0 Instance
1. Initial Position: An unauthenticated attacker sends an HTTP GET request to the Ech0 instance with a specially crafted Accept-Language header containing a large number of `_` characters.
2. Triggering the Flaw: The i18n middleware processes the request and passes the Accept-Language header to `goi18n.NewLocalizer`, which internally calls `language.ParseAcceptLanguage`. The parser's quadratic-time behavior is triggered due to the large number of `_` characters.
3. What Breaks: The security boundary fails because the CVE-2022-32149 guard is bypassed due to the use of `_` characters, allowing the parser to consume excessive CPU resources.
4. Attacker's Prize: The attacker can cause significant CPU consumption, potentially pinning 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 can saturate a 10-core Ech0 instance indefinitely while consuming ~10 MiB/s of upstream bandwidth.
Real-World Impact
The impact of this vulnerability is significant, as it allows an unauthenticated attacker to cause a denial-of-service (DoS) attack on the Ech0 instance. This can lead to:
- CPU consumption amplification of ~70x.
- Potential saturation of CPU cores.
- Increased upstream bandwidth consumption.
Detection & Defense
Immediate Mitigations
To mitigate this vulnerability, apply the following fixes:
- Upgrade to a patched version of Ech0 (if available).
- Apply a size and character-class filter at the i18n middleware boundary to cap the number of `_` and `-` characters in the Accept-Language header.
Example of a fix:
```go
const maxAcceptLanguageSeparators = 32
func sanitizeAcceptLanguage(v string) string {
if strings.Count(v, "-")+strings.Count(v, "_") > maxAcceptLanguageSeparators {
return ""
}
return v
}
func Middleware() gin.HandlerFunc {
return func(ctx *gin.Context) {
explicit := explicitLocaleFromRequest(ctx)
acceptLanguage := sanitizeAcceptLanguage(strings.TrimSpace(ctx.GetHeader("Accept-Language")))
locale := systemDefaultLocale()
if explicit != "" {
locale = ResolveLocale(explicit, acceptLanguage)
}
setLocaleContext(ctx, locale, acceptLanguage)
ctx.Next()
}
}
```
Detection Strategies
To detect exploitation attempts, monitor for:
- Unusually large Accept-Language headers.
- Requests with an excessive number of `_` or `-` characters in the Accept-Language header.
- Unauthenticated requests causing significant CPU consumption.
Long-Term Hardening
To prevent similar vulnerabilities, implement:
- Input validation and sanitization for all user-supplied data.
- Size and character-class filtering for headers.
- Regular security updates and patches for dependencies.
Key Takeaways
- The Ech0 ParseAcceptLanguage vulnerability allows for a ~70x CPU amplification via the Accept-Language header.
- The vulnerability is caused by the lack of input validation and sanitization in the i18n middleware.
- An unauthenticated attacker can cause significant CPU consumption, potentially leading to a DoS attack.
- Apply immediate mitigations, such as input filtering, and consider long-term hardening strategies to prevent similar vulnerabilities.
Sources
- GitHub Security Advisories: https://github.com/advisories/GHSA-mqxv-9rm6-w8qc