CVE-2026-109821
Unbounded port parsing in URI.parse/1 enables CPU exhaustion denial of service in Elixir
- State
- Published
- Severity
- 6.3 Medium
- Published
- Oct 30, 2026
- Updated
- Oct 30, 2026
- Reserved
- Oct 23, 2026
Description
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 6.3 Medium | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N | EEF |
Weaknesses
Affected Products
| Product | Versions |
|---|---|
elixirelixir-lang |
|
elixirelixir-lang |
|
References
- Unbounded port parsing in URI.parse/1 enables CPU exhaustion denial of servicevendor-advisoryrelated
- EEF CNA record for CVE-2026-109821related
- OSV record EEF-CVE-2026-109821related
- Erlang/OTP advisory for the same issue in uri_stringrelated
- Introducing commit 3980182 in elixir-lang/elixirrelated
- Fix commit 9a39d64 in elixir-lang/elixirpatch
- Fix commit b70f33a in elixir-lang/elixirpatch
- Fix commit 07d9abc in elixir-lang/elixirpatch
- Fix commit d879b39 in elixir-lang/elixirpatch
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