Summary
Tesla has decompression bomb on response body
Any Tesla client pipeline that includes Tesla.Middleware.DecompressResponse or Tesla.Middleware.Compression eagerly decompresses HTTP response bodies with no size limit. A server under attacker control (or reached via a redirect) can return a tiny gzip-encoded payload that expands into gigabytes of BEAM heap, crashing or freezing the calling process. Stacking multiple content-encoding tokens multiplies the amplification exponentially.
Details
decompress_body/2 in lib/tesla/middleware/compression.ex passes the full response body to :zlib.gunzip/1 or :zlib.unzip/1 with no cap on output size. The list of codec tokens comes from splitting the content-encoding header on commas, and decompress_body/2 recurses once per token. A response advertising content-encoding: gzip, gzip, gzip, gzip triggers four recursive decompression passes. Each gzip layer can expand its input roughly 1000x, so a 284-byte wire payload with four layers inflates to approximately 1 GB at the innermost pass, all materialised as a single binary in the caller's heap.
PoC
- Serve an HTTP response with
content-encoding: gzip, gzip, gzip, gzipwhere the body is a 1 GB block of zeros compressed through four successive gzip passes. - Send that response to a Tesla client whose pipeline includes
Tesla.Middleware.DecompressResponse. decompress_body/2recurses four times without any size check, materialising ~1 GB in the calling process's heap.- Repeated or sufficiently large requests exhaust available memory and crash or freeze the node.
Configurations
The application must include Tesla.Middleware.DecompressResponse or Tesla.Middleware.Compression in its Tesla middleware pipeline.
Resources
Impact
High severity (CVSS v4.0: 8.2). Any application using tesla 0.6.0 through 1.18.2 with Tesla.Middleware.DecompressResponse or Tesla.Middleware.Compression in its pipeline is vulnerable. The attacker only needs to control a server the client contacts, including via redirects. Fixed in tesla 1.18.3.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-48594? CVE-2026-48594 is a high-severity security vulnerability in tesla (erlang), affecting versions >= 0.6.0, < 1.18.3. It is fixed in 1.18.3.
- Which versions of tesla are affected by CVE-2026-48594? tesla (erlang) versions >= 0.6.0, < 1.18.3 is affected.
- Is there a fix for CVE-2026-48594? Yes. CVE-2026-48594 is fixed in 1.18.3. Upgrade to this version or later.
- Is CVE-2026-48594 exploitable, and should I be worried? Whether CVE-2026-48594 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-48594 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-48594? Upgrade
teslato 1.18.3 or later.