# CVE-2026-45409: Internationalized Domain Names in Applications (IDNA): Specially crafted inputs to idna.encode() can bypass CVE-2024-3651 fix > Attackers can cause denial of service in applications using the Python IDNA library by sending specially crafted inputs that consume excessive resources. - **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 5 Jun 2026 - **Updated:** 8 Jun 2026 - **Also known as:** ALSA-2026:54290, ALSA-2026:54481, ALSA-2026:54484, BELL-CVE-2026-45409, CLEANSTART-2026-CS22541, CLEANSTART-2026-WY69230, CLSA-2026-1789456194, CLSA-2026-1791363492, CLSA-2026-1791364869, CLSA-2026-1791530173, DEBIAN-CVE-2026-45409, ECHO-b5f1-63a7-4f7c, GHSA-65pc-fj4g-8rjx, MINI-387g-rh74-8p3p, MINI-4979-x2qq-c9gv, MINI-55rp-4r6w-2v7j, MINI-742r-g643-mcgx, MINI-75m3-wm3v-v4mm, MINI-7f68-35wx-2923, MINI-85p2-vxrx-rw66, MINI-85v5-wxxq-9wr7, MINI-999f-wwv9-g642, MINI-9q5x-h9xx-c8pq, MINI-f773-9rw3-xx9x, MINI-g997-p96r-r665, MINI-g99j-24v3-2vw6, MINI-gp8m-6wh5-jv6v, MINI-gppf-hj28-xgrm, MINI-hp6w-53pw-mqmq, MINI-hx7v-m3r6-6mc9, MINI-jphw-9vrx-crc3, MINI-mhhj-3765-89vr, MINI-p575-534x-pwqj, MINI-q52m-9pg9-6mcx, MINI-qf9g-22xx-36rv, MINI-vmwv-fpjr-wwcc, MINI-w3rw-c9x2-5r2f, MINI-wrq6-mw27-fq49, MINI-x28q-8g6x-j464, MINI-x9rw-63qc-m83v, OESA-2026-2605, PYSEC-2026-215, RHSA-2026:25503, RHSA-2026:54290, RHSA-2026:54481, RHSA-2026:54484, RLSA-2026:54290, RLSA-2026:54481, RLSA-2026:54484, ROOT-APP-PYPI-CVE-2026-45409, SUSE-SU-2026:21873-1, SUSE-SU-2026:21914-1, SUSE-SU-2026:22271-1, SUSE-SU-2026:22356-1, SUSE-SU-2026:2828-1, SUSE-SU-2026:3100-1, SUSE-SU-2026:3101-1, UBUNTU-CVE-2026-45409, USN-8549-1, openSUSE-SU-2026:10829-1, openSUSE-SU-2026:21048-1 ## What is CVE-2026-45409? CVE-2026-45409 is a medium-severity denial of service vulnerability in kjd idna, published on 5 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description Internationalized Domain Names in Applications (IDNA) for Python provides support for Internationalized Domain Names in Applications (IDNA) and Unicode IDNA Compatibility Processing. In versions prior to 3.15, payloads such as `"\u0660" * N` or `"\u30fb" * N + "\u6f22"` utilize the `valid_contexto` function prior to length rejection, and for high values of `N` will take a long time to process. This is the same issue as CVE-2024-3651, however the original remediation in 2024 was not a complete fix. A specially crafted argument to the `idna.encode()` function could consume significant resources. This may lead to a denial-of-service. Starting in version 3.14, the function rejects long inputs as soon as practicable prior to any further processing to minimize resource consumption. In version 3.15, this approach was extended to lesser used alternate functions (i.e. per-label conversions and codec support). A workaround is available. Domain names cannot exceed 253 characters in length. If this length limit is enforced prior to passing the domain to the `idna.encode()` function, it should no longer consume significant resources. This is triggered by arbitrarily large inputs that would not occur in normal usage, but may be passed to the library assuming there is no preliminary input validation by the higher-level application. Weakness: CWE-1333 (Inefficient Regular Expression Complexity) ## Which versions are affected by CVE-2026-45409? 3 open source packages ship an affected version, including idna. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `idna` | PyPI | All versions | 3.15 | | `idna` | PyPI | All versions | 3.15 | | `idna` | PyPI | All versions | 3.15 | | `python3-idna` | AlmaLinux:10 | All versions | 3.7-6.el10_2 | | `python3-idna` | AlmaLinux:8 | All versions | 2.5-8.el8_10 | | `python3-idna` | AlmaLinux:9 | All versions | 2.10-8.el9_8 | | `python-idna` | Red Hat:enterprise_linux:10.2 | All versions | 0:3.7-6.el10_2 | | `python3-idna` | Red Hat:enterprise_linux:10.2 | All versions | 0:3.7-6.el10_2 | | `python-idna` | Red Hat:enterprise_linux:8::baseos | All versions | 0:2.5-8.el8_10 | | `python3-idna` | Red Hat:enterprise_linux:8::baseos | All versions | 0:2.5-8.el8_10 | | `python-idna` | Red Hat:enterprise_linux:9::baseos | All versions | 0:2.10-8.el9_8 | | `python3-idna` | Red Hat:enterprise_linux:9::baseos | All versions | 0:2.10-8.el9_8 | | `python-idna` | Red Hat:hummingbird:1 | All versions | 0:3.18-1.hum1 | | `python3-idna` | Red Hat:hummingbird:1 | All versions | 0:3.18-1.hum1 | | `python-idna` | Rocky Linux:10 | All versions | 0:3.7-6.el10_2 | | `python-idna` | Rocky Linux:8 | All versions | 0:2.5-8.el8_10 | | `python-idna` | Rocky Linux:9 | All versions | 0:2.10-8.el9_8 | | `python-idna` | SUSE:Linux Enterprise Micro 5.3 | All versions | 2.6-150000.3.9.1 | | `python-idna` | SUSE:Linux Enterprise Micro 5.4 | All versions | 2.6-150000.3.9.1 | | `python-idna` | SUSE:Linux Enterprise Micro 5.5 | All versions | 2.6-150000.3.9.1 | | `python-idna` | SUSE:Linux Enterprise Module for Basesystem 15 SP7 | All versions | 2.6-150000.3.9.1 | | `python-idna` | SUSE:Linux Enterprise Module for Public Cloud 12 | All versions | 2.5-3.16.1 | | `python-idna` | SUSE:Linux Enterprise Module for Public Cloud 15 SP4 | All versions | 3.4-150400.11.13.1 | | `python-idna` | SUSE:Linux Enterprise Module for Python 3 15 SP7 | All versions | 3.4-150400.11.13.1 | | `python-idna` | SUSE:Linux Enterprise Server 16.0 | All versions | 3.10-160000.3.1 | | `python-idna` | SUSE:Linux Enterprise Server LTSS Extended Security 12 SP5 | All versions | 2.5-3.16.1 | | `python-idna` | SUSE:Linux Enterprise Server for SAP applications 16.0 | All versions | 3.10-160000.3.1 | | `python-idna` | SUSE:Linux Micro 6.2 | All versions | 3.10-160000.3.1 | | `python-idna` | openSUSE:Leap 16.0 | All versions | 3.10-160000.3.1 | | `python-idna` | openSUSE:Tumbleweed | All versions | 3.15-1.1 | Products: Kjd Internationalized Domain Names in Applications. ## How do I fix CVE-2026-45409? Upgrade idna to 3.15 or later. ## Is CVE-2026-45409 being exploited? There is no known exploitation of CVE-2026-45409 in the wild and no public exploit code. ## Other vulnerabilities in kjd idna - [CVE-2024-3651](https://insights.sbomify.com/CVE-2024-3651/): Denial of Service via Quadratic Complexity in kjd/idna (medium 6.2) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-45409 and fix it if it is affected. What it is: CVE-2026-45409 is a medium-severity denial of service vulnerability in kjd idna, published on 5 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-45409 in the wild and no public exploit code. Affected packages and fixed versions: - idna (PyPI): affected all versions; fixed in 3.15 - idna (PyPI): affected all versions; fixed in 3.15 - idna (PyPI): affected all versions; fixed in 3.15 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-45409/ (Markdown: https://insights.sbomify.com/CVE-2026-45409/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45409 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45409 - OSV: https://osv.dev/vulnerability/CVE-2026-45409 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-45409/ Summaries are generated and may contain mistakes; the official description above is the record.