CVE-2026-90798 in CouchDB
Summary
by MITRE • 10/20/2026
A missing circuit-breaker in the replicator in Apache CouchDB 3.5.2 and below on all platforms allows the owner of a replication source or target to cause a denial of service via creating an infinite HTTP redirect loop.
Users are recommended to upgrade to version 3.5.3, which fixes this issue.
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Analysis
by VulDB Data Team • 10/20/2026
The vulnerability identified in Apache CouchDB versions prior to 3.5.3 stems from the absence of circuit-breaker mechanisms within the replication subsystem. This architectural oversight allows an authenticated user who controls either the source or target endpoint of a replication task to engineer a scenario that results in a denial of service condition. Specifically, by manipulating the configuration parameters associated with the replication process, an attacker can induce infinite HTTP redirect loops between CouchDB instances or nodes. The system lacks the necessary logic to detect and terminate these recursive redirection sequences, leading to continuous resource consumption without any mechanism for automatic recovery or timeout enforcement within this specific context.
From a technical perspective, the flaw resides in how the replicator handles responses during data synchronization operations. When replication is configured with certain endpoints that return redirect status codes, such as 301 Moved Permanently or 302 Found, CouchDB attempts to follow these redirects automatically to ensure data consistency across distributed nodes. However, without a circuit-breaker pattern implemented to limit the depth of recursion or track visited URLs within a single replication cycle, an attacker can craft a configuration where two endpoints point at each other in a circular manner. This creates an infinite loop that consumes CPU cycles and memory resources on the server handling the request, effectively rendering the service unavailable for legitimate operations until the process is manually terminated or crashes due to resource exhaustion.
The operational impact of this vulnerability is significant as it directly compromises the availability component of the CIA triad. An attacker does not require high-level administrative privileges; possession of credentials with replication rights on either end of a connection is sufficient to exploit this flaw. The resulting denial of service can disrupt data synchronization pipelines, cause latency spikes for other concurrent requests due to resource contention, and potentially lead to server instability if the memory consumption becomes severe enough. This poses a risk particularly in environments where CouchDB is used as a critical backend for applications requiring high availability and consistent real-time data replication across multiple nodes or geographic locations.
To mitigate this vulnerability, organizations running Apache CouchDB must upgrade immediately to version 3.5.3 or later, which includes the necessary fixes to implement circuit-breaking logic within the replicator module. This update ensures that infinite redirect loops are detected and aborted before they can consume excessive system resources. In addition to upgrading, administrators should review replication configurations to ensure that endpoints do not inadvertently create circular dependencies. Monitoring tools should be employed to detect unusual patterns of HTTP redirects or high CPU usage associated with replication tasks, providing an additional layer of defense against potential exploitation attempts while the upgrade is being deployed across the infrastructure.
This issue aligns with CWE-835, which describes looping issues that can lead to resource exhaustion and denial of service conditions. Furthermore, from a threat modeling perspective using the MITRE ATT&CK framework, this vulnerability facilitates Denial of Service (T1499) by leveraging application logic flaws rather than network-level attacks. The exploitation method falls under T1053 Scheduled Task/Job, as it involves manipulating scheduled or triggered replication processes to degrade system performance. Understanding these classifications helps security teams prioritize remediation efforts and adjust detection rules within their intrusion detection systems to identify similar patterns of abuse in other distributed database environments.