Elixir-Tesla - CraftedSignal Threat Feed

Tesla Elixir Client Decompression Bomb (CVE-2026-48594)

hello@craftedsignal.io — Fri, 10 Jul 2026 00:08:28 +0000

A high-severity vulnerability, tracked as CVE-2026-48594, exists in the Tesla Elixir HTTP client library, specifically affecting versions 0.6.0 through 1.18.2. This flaw, dubbed a "decompression bomb," can be exploited by an attacker who controls a server that a vulnerable Tesla client contacts, or via a redirect. The vulnerability arises when the Tesla.Middleware.DecompressResponse or Tesla.Middleware.Compression middleware component eagerly decompresses HTTP response bodies without any size limits. An attacker can craft a minuscule gzip-encoded payload coupled with multiple content-encoding headers (e.g., gzip, gzip, gzip, gzip), which, upon recursive decompression, expands exponentially into gigabytes of data on the BEAM heap. This excessive memory consumption inevitably leads to the client application crashing or freezing, effectively causing a denial of service. Defenders must ensure that applications utilizing the affected tesla library are patched to version 1.18.3 or later to mitigate this risk.

Attack Chain

An attacker gains control of a server or compromises a legitimate server that a victim's Tesla client application is likely to contact.
The attacker configures the server to serve a specially crafted HTTP response.
The crafted response includes a tiny gzip-compressed payload that is designed to expand significantly upon decompression.
Crucially, the response features multiple content-encoding headers, such as gzip, gzip, gzip, gzip, to trigger recursive decompression.
A legitimate application, running an affected tesla library version (0.6.0 to 1.18.2) and configured with Tesla.Middleware.DecompressResponse or Tesla.Middleware.Compression, makes an HTTP request to the attacker-controlled server.
The tesla client receives the malicious HTTP response from the attacker's server.
The decompress_body/2 function within the tesla middleware attempts to decompress the response recursively for each content-encoding token, without any output size validation.
This process exponentially inflates the small payload into gigabytes of data within the BEAM heap, exhausting the application's memory resources and causing it to crash or freeze, resulting in a denial of service.

Impact

The impact of CVE-2026-48594 is a denial of service (DoS) for any application utilizing the affected tesla client library (versions 0.6.0 through 1.18.2) with the Tesla.Middleware.DecompressResponse or Tesla.Middleware.Compression middleware. The attacker's objective is to render the targeted application unusable by forcing it to consume all available memory. A successful attack can lead to application downtime, data processing failures, and disruption of critical services, potentially affecting any sector relying on Elixir applications performing HTTP requests with the vulnerable middleware. This vulnerability carries a high severity CVSS v4.0 score of 8.2.

Recommendation

Patch CVE-2026-48594 by upgrading the erlang/tesla package to version 1.18.3 or later immediately.
Review applications for the inclusion of Tesla.Middleware.DecompressResponse or Tesla.Middleware.Compression in their Tesla middleware pipeline. If present, ensure they are running patched versions.
Implement application-level monitoring for abnormal and sudden increases in memory consumption by Elixir applications, especially those making outbound HTTP requests, to detect potential exploitation attempts.

Tesla HTTP Client Library Vulnerable to Atom Exhaustion Leading to Denial of Service (CVE-2026-48597)

hello@craftedsignal.io — Fri, 10 Jul 2026 00:07:00 +0000

An unauthenticated attacker can trigger a remote denial-of-service (DoS) condition in applications utilizing the erlang/tesla HTTP client library, specifically when configured with Tesla.Adapter.Mint. This vulnerability, identified as CVE-2026-48597, affects Tesla versions from 1.3.0 up to 1.18.2. The flaw stems from Tesla.Adapter.Mint.open_conn/2 passing untrusted URL schemes directly to String.to_atom/1 without validation. As BEAM (Erlang Virtual Machine) atoms are permanent and its atom table has a finite capacity of approximately 1,048,576 entries, repeatedly supplying unique, non-standard URL schemes (e.g., atk1://, atk2://) causes the VM to continuously mint new atoms. This eventually exhausts the atom table, leading to an immediate crash of the Elixir/Erlang VM and consequently, the affected application. This attack requires no special privileges beyond the ability to send HTTP requests to a vulnerable application endpoint that processes user-supplied URLs or leverages Tesla.Middleware.FollowRedirects.

Attack Chain

An attacker identifies an application using erlang/tesla versions 1.3.0 through 1.18.2 with Tesla.Adapter.Mint configured, and which exposes an endpoint that processes user-supplied URLs (e.g., a webhook relay, link preview service, or SSRF-style proxy) or includes Tesla.Middleware.FollowRedirects in its pipeline.
The attacker sends an HTTP request to the vulnerable application, including a URL with a novel, non-standard scheme (e.g., atk1://attacker.com/path) in a parameter that the application forwards to the Tesla HTTP client.
The Tesla.Adapter.Mint.open_conn/2 function receives this untrusted URL and extracts the scheme (e.g., "atk1").
The extracted scheme is passed directly to String.to_atom/1, which creates and interns a new, permanent atom in the BEAM VM's atom table.
Although the Mint library subsequently rejects the connection attempt due to the unrecognized scheme, the newly created atom persists in the VM's global atom table.
The attacker repeats steps 2-5, sending approximately 1,000,000 requests, each with a distinct and previously unused URL scheme (e.g., atk2://, atk3://, etc.).
Upon reaching the BEAM VM's atom table capacity limit (roughly 1,048,576 entries), the String.to_atom/1 call fails, leading to a fatal error that crashes the entire Elixir/Erlang VM.
The application hosting the Tesla client becomes unavailable, resulting in a remote denial-of-service condition.

Impact

This high-severity vulnerability (CVSS v4.0: 8.2) allows an unauthenticated attacker to remotely trigger a complete denial of service for any application using erlang/tesla versions 1.3.0 through 1.18.2 with the Tesla.Adapter.Mint adapter. The attack results in a crash of the underlying BEAM Virtual Machine, making the affected application entirely unavailable. No specific victim count or targeted sectors have been publicly identified, but any Elixir application fitting the criteria that processes untrusted URL input is at risk.

Recommendation

Patch erlang/tesla to version 1.18.3 or later immediately to remediate CVE-2026-48597.
Review any application features that forward untrusted URLs through Tesla.Adapter.Mint and implement robust input validation or allow-listing for URL schemes before passing them to the Tesla client.
If Tesla.Middleware.FollowRedirects is used in conjunction with untrusted inputs, ensure that redirect targets are properly validated and schemes are restricted to http(s) to prevent exploitation via malicious Location headers.