Vulnerability · Published Oct 30, 2026 · Assigned by EEF
CVE-2026-109821Unbounded port parsing in URI.parse/1 enables CPU exhaustion denial of service in Elixir
Medium 6.3
In plain English
A medium-severity uncontrolled resource consumption in elixir from elixir-lang. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 43% of all known vulnerabilities).
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | elixir-lang | no fix listed | DEBIAN-CVE-2026-109821 |
| Debian:13 | elixir-lang | no fix listed | DEBIAN-CVE-2026-109821 |
| Debian:14 | elixir-lang | no fix listed | DEBIAN-CVE-2026-109821 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| elixir-lang | elixir | 0.5.0 – before 1.18.61.19.0-rc.0 – before 1.19.71.20.0-rc.0 – before 1.20.5 |
| elixir-lang | elixir | 39801821eef2d06524e5ebf5a0e4b3c380ad23ae – before * |
Weakness: CWE-1284, CWE-400 · Vector: 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
References
- Unbounded port parsing in URI.parse/1 enables CPU exhaustion denial of service vendor-advisory, related
- EEF CNA record for CVE-2026-109821 related
- OSV record EEF-CVE-2026-109821 related
- Erlang/OTP advisory for the same issue in uri_string related
- Introducing commit 3980182 in elixir-lang/elixir related
- Fix commit 9a39d64 in elixir-lang/elixir patch
- Fix commit b70f33a in elixir-lang/elixir patch
- Fix commit 07d9abc in elixir-lang/elixir patch
- Fix commit d879b39 in elixir-lang/elixir patch