CVE-2022-21698 in client_golang
Summary
by MITRE • 02/15/2022
client_golang is the instrumentation library for Go applications in Prometheus, and the promhttp package in client_golang provides tooling around HTTP servers and clients. In client_golang prior to version 1.11.1, HTTP server is susceptible to a Denial of Service through unbounded cardinality, and potential memory exhaustion, when handling requests with non-standard HTTP methods. In order to be affected, an instrumented software must use any of `promhttp.InstrumentHandler*` middleware except `RequestsInFlight`; not filter any specific methods (e.g GET) before middleware; pass metric with `method` label name to our middleware; and not have any firewall/LB/proxy that filters away requests with unknown `method`. client_golang version 1.11.1 contains a patch for this issue. Several workarounds are available, including removing the `method` label name from counter/gauge used in the InstrumentHandler; turning off affected promhttp handlers; adding custom middleware before promhttp handler that will sanitize the request method given by Go http.Request; and using a reverse proxy or web application firewall, configured to only allow a limited set of methods.
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Analysis
by VulDB Data Team • 03/16/2026
The vulnerability described in CVE-2022-21698 affects the client_golang instrumentation library used in Prometheus monitoring systems, specifically within the promhttp package that handles HTTP server and client operations. This issue represents a denial of service vulnerability that can lead to memory exhaustion through unbounded cardinality when processing HTTP requests with non-standard methods. The flaw exists in versions prior to 1.11.1 of the client_golang library, making it a critical concern for organizations relying on Prometheus instrumentation for their monitoring infrastructure.
The technical implementation of this vulnerability stems from how the instrumentation middleware processes HTTP requests containing unconventional HTTP methods. When applications use promhttp.InstrumentHandler* middleware functions without proper method filtering, the library creates metrics with method labels that can grow indefinitely based on the variety of request methods encountered. This unbounded cardinality in metric labels directly translates to memory consumption that increases without limit, creating a potential vector for denial of service attacks. The vulnerability specifically impacts the InstrumentHandlerCounter and InstrumentHandlerDuration functions which track metrics based on HTTP methods, as documented under CWE-400 which addresses unchecked resource consumption in software systems.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise entire monitoring infrastructures. Organizations using Prometheus instrumentation for their applications face the risk of memory exhaustion attacks that could render their monitoring systems unusable, affecting incident response and system observability capabilities. The attack surface is particularly concerning because it requires minimal effort to exploit - simply sending requests with unusual HTTP methods to an instrumented application can trigger the memory exhaustion behavior. This vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under T1499.004 for resource exhaustion and T1566.001 for phishing with malicious attachments, though the specific exploitation vector is more subtle and system-level.
Mitigation strategies for this vulnerability include upgrading to client_golang version 1.11.1 which contains the official patch addressing the unbounded cardinality issue. Organizations can also implement several workarounds including removing the method label from counters and gauges used in the instrumentation middleware, disabling the affected promhttp handlers, or implementing custom middleware to sanitize HTTP request methods before they reach the instrumentation layer. Additionally, deploying reverse proxies or web application firewalls that filter HTTP methods to only allow standard ones provides an effective defense mechanism. The vulnerability highlights the importance of proper input validation and resource management in monitoring tooling, aligning with security principles from NIST SP 800-53 and ISO/IEC 27001 standards that emphasize protecting against resource exhaustion and ensuring robust input validation in system components.