CVE-2026-82760 in ash_authentication
Summary
by MITRE • 09/17/2026
Inefficient Algorithmic Complexity vulnerability in team-alembic AshAuthentication allows an unauthenticated attacker to exhaust CPU and memory via an oversized base62 segment in a submitted API key.
AshAuthentication.Base.decode62/1 in lib/ash_authentication/base.ex splits its argument into one binary per character and folds it with charval62/2, which recomputes Integer.pow(62, index) at every position instead of accumulating by Horner's method, so cost grows roughly cubically in the input length. bindecode62/1 in the same module is quadratic through Integer.undigits/2 and Integer.digits/2. Neither function caps byte_size/1, and AshAuthentication.Strategy.ApiKey.SignInPreparation passes the underscore-separated segments of the submitted key straight into both, before any key lookup and without prior authentication. The surrounding rescue clauses catch exceptions, not CPU or memory exhaustion.
This issue affects ash_authentication: from 4.8.0 before 4.15.0 and from 5.0.0-rc.0 before 5.0.0-rc.14.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in the AshAuthentication library, specifically within versions ranging from 4.8.0 up to but not including 4.15.0 and from 5.0.0-rc.0 prior to 5.0.0-rc.14, represents a critical inefficiency in algorithmic complexity that leads to resource exhaustion attacks. This flaw is rooted in the implementation of base62 decoding functions used during the authentication process for API keys. The core issue lies within the AshAuthentication.Base module, where two primary functions, decode62/1 and bindecode62/1, exhibit poor computational scaling relative to input size. These functions are invoked by the SignInPreparation strategy when processing submitted API keys, specifically handling underscore-separated segments of the key string before any actual authentication lookup or credential verification takes place. Because this processing occurs prior to establishing an authenticated session, it is accessible to unauthenticated actors who can exploit these inefficiencies to launch denial-of-service attacks against the application infrastructure.
The technical root cause in the decode62/1 function involves a fundamental misunderstanding of efficient integer conversion algorithms. Instead of utilizing Horner's method, which allows for linear time complexity by accumulating values through multiplication and addition in a single pass, the implementation recomputes Integer.pow(62, index) at every character position. This approach results in redundant calculations that grow cubically with respect to the input length. Furthermore, the function splits its argument into one binary per character before folding it with charval62/2, adding significant overhead related to memory allocation and garbage collection for each segment created. The lack of any cap on byte_size means there is no upper limit preventing an attacker from submitting arbitrarily large inputs that trigger this cubic growth pattern indefinitely until system resources are depleted.
Similarly, the bindecode62/1 function suffers from quadratic complexity due its reliance on Integer.undigits/2 and Integer.digits/2 operations without length constraints. These standard library functions perform conversions that scale poorly when applied to excessively long strings generated by malicious actors. The combination of these two inefficient decoding mechanisms within the authentication pipeline creates a severe performance bottleneck. When an attacker submits an API key containing oversized base62 segments, the system is forced to expend disproportionate amounts of CPU cycles and memory processing the input string rather than performing legitimate security checks or business logic operations. This inefficiency transforms what should be a lightweight pre-authentication step into a heavy computational burden that can easily overwhelm server resources.
The operational impact of this vulnerability is significant as it enables unauthenticated attackers to exhaust both central processing unit time and available memory on the hosting infrastructure. Since the surrounding rescue clauses in the code are designed to catch exceptions rather than monitor resource consumption or enforce timeouts, they do not mitigate the effects of CPU exhaustion. An attacker can repeatedly send requests with increasingly large base62 segments, causing the application threads to hang or crash due to excessive computation time and memory pressure. This effectively results in a denial-of-service condition where legitimate users are unable to access services because server resources are consumed by processing maliciously crafted inputs. The attack vector is straightforward as it requires no prior authentication, making it particularly dangerous for public-facing APIs that accept API keys directly from clients without initial identity verification.
From a classification perspective, this vulnerability aligns with CWE-400, which covers Uncontrolled Resource Consumption, and more specifically relates to algorithms with inefficient computational complexity leading to resource exhaustion. In the context of the MITRE ATT&CK framework, this behavior is consistent with techniques used in Denial-of-Service attacks where adversaries aim to disrupt availability by consuming system resources beyond their intended capacity. The specific mechanism involves exploiting algorithmic inefficiencies rather than buffer overflows or injection flaws, highlighting a gap in input validation and performance optimization within the authentication library's core decoding logic.
To mitigate this vulnerability, immediate updates to the AshAuthentication library are required for all affected versions. Users running version 4.x should upgrade to at least version 4.15.0, while those on the 5.0 release candidate track must update to version 5.0.0-rc.14 or later. These updated releases address the algorithmic inefficiencies by implementing proper bounds checking and optimizing the decoding processes to prevent cubic and quadratic scaling behaviors. In addition to upgrading dependencies, developers should implement rate limiting on authentication endpoints to restrict the number of login attempts per IP address over a given time window. This adds an additional layer of defense against automated abuse even if similar vulnerabilities exist in other components. Furthermore, integrating application-level timeouts for long-running operations can help prevent individual requests from monopolizing server threads indefinitely. Input validation should also be enforced at the API gateway or load balancer level to reject excessively large payloads before they reach the application logic, thereby reducing the attack surface and protecting backend resources from being overwhelmed by malformed inputs.