CVE-2026-109821

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CVE-2026-109821

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

Details: 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.

References: https://cna.erlef.org/cves/CVE-2026-109821.html, https://github.com, https://osv.dev/vulnerability/EEF-CVE-2026-109821, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/109xxx/CVE-2026-109821.json, https://github.com/elixir-lang/elixir/security/advisories/GHSA-327h-97cv-59xg, https://github.com/erlang/otp/security/advisories/GHSA-8qw4-2chm-mvj2, https://nvd.nist.gov/vuln/detail/CVE-2026-109821, https://github.com/elixir-lang/elixir/commit/07d9abc3f3ac4c8d2ba8384bd102b6d6205b08b7, https://github.com/elixir-lang/elixir/commit/39801821eef2d06524e5ebf5a0e4b3c380ad23ae, https://github.com/elixir-lang/elixir/commit/9a39d64a4473d02681c486bc70681c972479d32b, https://github.com/elixir-lang/elixir/commit/b70f33a591b6ab8eb0fa4a7e00bac1c2ed4e0d58, https://github.com/elixir-lang/elixir/commit/d879b39d778fec2f475689573d5672720c4f2a21, https://github.com/elixir-lang/elixir