CVE-2026-71848
ADVISORY - githubSummary
Summary
The languageDetector middleware is vulnerable to algorithmic complexity denial of service when processing a crafted language tag containing a large number of hyphen-separated subtags.
Details
To implement progressive language-tag truncation, normalizeLanguage() repeatedly calls parts.slice(0, i).join('-') for every possible prefix. The total amount of string processing grows quadratically with the number of subtags.
Language values may come from a query parameter, cookie, Accept-Language header, or URL path, depending on the detector configuration. The default detector order enables query-string, cookie, and header detection, so applications using languageDetector() may expose this processing to unauthenticated requests.
Request-size limits reduce the maximum cost of a single request but do not eliminate the issue. Inputs accepted by common JavaScript runtimes can still cause noticeable synchronous event-loop blocking.
Impact
An attacker may repeatedly send requests containing long, hyphen-separated language tags, causing excessive CPU consumption and preventing unrelated requests from being processed.
The practical impact depends on the runtime's request-size limits, reverse-proxy configuration, and the detectors enabled by the application.
Resolution
The progressive lookup should avoid reconstructing every shorter prefix. The implementation can instead inspect the configured supported languages and select the longest value that matches the input at a hyphen boundary.
Common Weakness Enumeration (CWE)
Inefficient Algorithmic Complexity
Inefficient Algorithmic Complexity
GitHub
3.9
CVSS SCORE
5.3medium| Package | Type | OS Name | OS Version | Affected Ranges | Fix Versions |
|---|---|---|---|---|---|
| hono | npm | - | - | >=4.12.0,<4.12.34 | 4.12.34 |
CVSS:3 Severity and metrics
The CVSS metrics represent different qualitative aspects of a vulnerability that impact the overall score, as defined by the CVSS Specification.
The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone). One example of an Adjacent attack would be an ARP (IPv4) or neighbor discovery (IPv6) flood leading to a denial of service on the local LAN segment (e.g., CVE-2013-6014).
Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.
The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
The vulnerable system can be exploited without interaction from any user.
An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
There is no loss of confidentiality.
There is no loss of trust or accuracy within the impacted component.
Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.
NIST
3.9