CVE-2026-48594: Elixir Tesla denial of service via decompression bomb in compression middleware

Executive brief

Tesla is a popular HTTP client library for the Elixir programming language. A vulnerability exists where the library fails to limit the size of decompressed data when receiving responses from a server. An attacker-controlled server can send a specially crafted, highly compressed 'decompression bomb' that expands to gigabytes in memory, causing the application to crash or freeze and resulting in a denial of service.

Technical details

The vulnerability exists in the `Tesla.Middleware.DecompressResponse` and `Tesla.Middleware.Compression` components. The `decompress_body/2` function in `lib/tesla/middleware/compression.ex` recursively calls `:zlib.gunzip/1` or `:zlib.unzip/1` based on the `content-encoding` header without enforcing any output size limits. By providing multiple encoding tokens (e.g., 'gzip, gzip, gzip'), an attacker can achieve exponential data amplification. A small network payload can thus materialize as gigabytes of data on the BEAM heap, leading to memory exhaustion (CWE-409). The issue is fixed in version 1.18.3.

Affected products

• elixir-tesla tesla >= 0.6.0, < 1.18.3

Timeline

• 2026-06-02: disclosed: Initial disclosure and NVD publication
• 2026-07-10: advisory: GitHub Advisory published/reviewed
• 1.18.3: patched

References

• https://api.github.com/users/PJUllrich
• https://github.com/PJUllrich
• https://api.github.com/users/PJUllrich/gists%7B/gist_id%7D
• https://api.github.com/users/PJUllrich/repos
• https://avatars.githubusercontent.com/u/10426523?v=4
• https://api.github.com/users/PJUllrich/events%7B/privacy%7D