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CVE-2026-79658 – Denial of Service (CPU Exhaustion) – Ech0 before v5.0.1

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Summary

CVE-2026-79658 is an uncontrolled resource consumption (denial-of-service) vulnerability in Ech0, a self-hosted application, affecting all versions before 5.0.1. The flaw resides in Ech0’s i18n middleware, which fails to bound the size or structure of the Accept-Language HTTP header before passing it to Go’s language-tag parser. A single unauthenticated, network-delivered request can force the server to burn excessive CPU time, and a small number of concurrent attackers can saturate a multi-core server.

Technical details

  • Root cause: the i18n middleware calls go-i18n’s NewLocalizer, which invokes golang.org/x/text/language.ParseAcceptLanguage. The parser’s internal scanner treats underscore (_) characters the same as hyphens (-), but Ech0 only limited the count of hyphens (per the earlier upstream fix for CVE-2022-32149), leaving underscore-separated tokens unrestricted.
  • Trigger conditions: an attacker sends a request with an Accept-Language header (up to ~1 MiB) composed of many underscore-separated tokens, invoking the parser’s quadratic-time (O(N²)) tag-splitting behavior (gobble function).
  • Attack vector: network, unauthenticated, no user interaction required; the malicious header can be sent to any endpoint that passes through the i18n middleware, and the response still returns HTTP 200, making the attack harder to spot via error-rate monitoring.
  • Impact: a single crafted request can consume roughly 1.5 seconds of CPU; combining it with an additional X-Locale header increases this further. A handful of concurrent attackers can exhaust CPU capacity on a multi-core server, denying service to legitimate users.

Affected software

  • Ech0 (github.com/lin-snow/Ech0) versions ≤ 4.8.2 (all versions prior to 5.0.1)
  • Fixed in version 5.0.1 and later

Severity

  • CVSS v3.1 Base Score: 7.5 (HIGH) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  • A CVSS v4.0 scoring of this issue has also been published at 8.7 (HIGH), reflecting the network-exploitable, low-complexity availability impact.

Mitigation and recommended actions

  • Immediate: upgrade Ech0 to version 5.0.1 or later, which restricts the size/structure of the Accept-Language header before it reaches the language parser.
  • If patching is not immediately possible: deploy a reverse proxy or WAF rule that caps Accept-Language (and similar locale-related headers such as X-Locale) header length and rejects headers containing excessive hyphen/underscore-separated tokens; monitor for abnormal CPU usage correlated with oversized locale headers.

References

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