Unbounded port parsing in URI.parse/1 enables CPU exhaustion denial of service in Elixir

Overview

Improper Validation of Specified Quantity in Input vulnerability in the Elixir standard library's URI module allows an attacker who supplies a URL to cause a denial of service through CPU exhaustion.

URI.parse/1 converts the port component with String.to_integer/1 in split_authority/1 (lib/elixir/lib/uri.ex) without bounding its length, so a port of up to 1,262,592 decimal digits produces a bignum of that size and a longer one raises SystemLimitError. Rendering the parsed URI back to text (URI.to_string/1, inspect/1, logging, error formatting) converts the bignum with :erlang.integer_to_binary/1, which is quadratic on Erlang/OTP 27, 28 and 29.0: a 400,000-digit port renders in about 2.6 seconds and a 1 MB port in about 18 seconds. Ports above 65535 are also accepted.

This issue affects elixir: from 0.5.0 before 1.18.6, from 1.19.0-rc.0 before 1.19.7, and from 1.20.0-rc.0 before 1.20.5.

Affected

• elixir >= 0.5.0 < 1.18.6
• elixir >= 1.19.0-rc.0 < 1.19.7
• elixir >= 1.20.0-rc.0 < 1.20.5
• elixir-lang/elixir >= 39801821eef2d06524e5ebf5a0e4b3c380ad23ae < *

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Workarounds

Reject long URLs before parsing them, for example anything above a few kilobytes, and reject a parsed port above 65535 before rendering or using the %URI{}. URI.new/1 is not affected on Erlang/OTP 27.3.4.17, 28.5.0.6, 29.0.6 and later, where :uri_string limits the port to 5 digits.