# CVE-2026-19553: SSLContext.wrap_bio() missing validation of server_hostname parameter > Attackers can bypass SSL hostname verification in Python applications if server_hostname is omitted, allowing man-in-the-middle attacks despite enabled checks. - **Severity:** High 7.6 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** A user has to click or open something - **Fix available:** Yes - **Published:** 30 Sep 2026 - **Updated:** 16 Oct 2026 - **Also known as:** ALPINE-CVE-2026-19553, AZL-105687, AZL-105918, BELL-CVE-2026-19553, BIT-libpython-2026-19553, BIT-python-2026-19553, BIT-python-min-2026-19553, CLSA-2026-1791825473, DEBIAN-CVE-2026-19553, ECHO-6954-9e11-de68, GHSA-xx9w-qm94-hghj, MINI-7r7j-v533-39x5, MINI-8qx6-5h26-w627, MINI-g6pr-qp62-r4h5, MINI-h29w-w255-v8qg, MINI-jhjj-8526-pqfq, OESA-2026-4525, OESA-2026-4588, OESA-2026-4589, OESA-2026-4590, PSF-2026-44, RHSA-2026:74587, RHSA-2026:74594, RHSA-2026:74599, RHSA-2026:74605, RHSA-2026:74606, ROOT-OS-DEBIAN-13-CVE-2026-19553, UBUNTU-CVE-2026-19553 ## What is CVE-2026-19553? CVE-2026-19553 is a high-severity vulnerability in CPython, published on 30 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link. ### Official description ssl.SSLContext.wrap_bio() didn't require the server_hostname argument to not be None if ssl.SSLContext.check_hostname was set. Due to a missing parameter check in SSLObject, if the server_hostname argument isn't supplied then hostname verification would be silently skipped. This defect could lead to programs where certificate hostname verification *appeared* to be succeeding with SSLContext.check_hostname = True and no ValueError being raised due to misconfiguration. If the program passes a server_hostname value that isn't an empty string or None to any of these APIs then certificate hostname verification proceeds as expected and the program is not affected by this vulnerability. Mitigating this vulnerability doesn't require updating Python or applying the patch. To mitigate, pass a valid non-None and non-empty server_hostname value to SSLContext.wrap_bio(), asyncio.create_connection(), or asyncio.loop.start_tls() and certificate hostname verification will proceed as expected. Upgrading to the latest version of Python or applying the patch only changes the behavior from silently skipping hostname verification to raising a ValueError, similar to SSLContext.wrap_socket(), when server_hostname isn't supplied. Weakness: CWE-297 (Improper Validation of Certificate with Host Mismatch) ## Which versions are affected by CVE-2026-19553? 3 open source packages ship an affected version, including libpython, python and python-min. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `libpython` | Bitnami | All versions | 3.10.22, 3.11.17, 3.12.15, 3.13.16, 3.14.8 | | `python` | Bitnami | All versions | 3.10.22, 3.11.17, 3.12.15, 3.13.16, 3.14.8 | | `python-min` | Bitnami | All versions | 3.10.22, 3.11.17, 3.12.15, 3.13.16, 3.14.8 | | `python-unversioned-command` | Red Hat:hummingbird:1 | All versions | 0:3.14.7-1.3.hum1 | | `python3` | Red Hat:hummingbird:1 | All versions | 0:3.14.7-1.3.hum1 | | `python3-debug` | Red Hat:hummingbird:1 | All versions | 0:3.14.7-1.3.hum1 | | `python3-devel` | Red Hat:hummingbird:1 | All versions | 0:3.14.7-1.3.hum1 | | `python3-idle` | Red Hat:hummingbird:1 | All versions | 0:3.14.7-1.3.hum1 | | `python3-libs` | Red Hat:hummingbird:1 | All versions | 0:3.14.7-1.3.hum1 | | `python3-test` | Red Hat:hummingbird:1 | All versions | 0:3.14.7-1.3.hum1 | | `python3-tkinter` | Red Hat:hummingbird:1 | All versions | 0:3.14.7-1.3.hum1 | | `python3.10` | Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.5.hum1 | | `python3.10-debug` | Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.5.hum1 | | `python3.10-devel` | Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.5.hum1 | | `python3.10-idle` | Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.5.hum1 | | `python3.10-libs` | Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.5.hum1 | | `python3.10-test` | Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.5.hum1 | | `python3.10-tkinter` | Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.5.hum1 | | `python3.11` | Red Hat:hummingbird:1 | All versions | 0:3.11.16-1.5.hum1 | | `python3.11-debug` | Red Hat:hummingbird:1 | All versions | 0:3.11.16-1.5.hum1 | | `python3.11-devel` | Red Hat:hummingbird:1 | All versions | 0:3.11.16-1.5.hum1 | | `python3.11-idle` | Red Hat:hummingbird:1 | All versions | 0:3.11.16-1.5.hum1 | | `python3.11-libs` | Red Hat:hummingbird:1 | All versions | 0:3.11.16-1.5.hum1 | | `python3.11-test` | Red Hat:hummingbird:1 | All versions | 0:3.11.16-1.5.hum1 | | `python3.11-tkinter` | Red Hat:hummingbird:1 | All versions | 0:3.11.16-1.5.hum1 | | `python3.12` | Red Hat:hummingbird:1 | All versions | 0:3.12.14-1.4.hum1 | | `python3.12-debug` | Red Hat:hummingbird:1 | All versions | 0:3.12.14-1.4.hum1 | | `python3.12-devel` | Red Hat:hummingbird:1 | All versions | 0:3.12.14-1.4.hum1 | | `python3.12-idle` | Red Hat:hummingbird:1 | All versions | 0:3.12.14-1.4.hum1 | | `python3.12-libs` | Red Hat:hummingbird:1 | All versions | 0:3.12.14-1.4.hum1 | | `python3.12-test` | Red Hat:hummingbird:1 | All versions | 0:3.12.14-1.4.hum1 | | `python3.12-tkinter` | Red Hat:hummingbird:1 | All versions | 0:3.12.14-1.4.hum1 | | `python3.13` | Red Hat:hummingbird:1 | All versions | 0:3.13.15-1.4.hum1 | | `python3.13-debug` | Red Hat:hummingbird:1 | All versions | 0:3.13.15-1.4.hum1 | | `python3.13-devel` | Red Hat:hummingbird:1 | All versions | 0:3.13.15-1.4.hum1 | | `python3.13-freethreading` | Red Hat:hummingbird:1 | All versions | 0:3.13.15-1.4.hum1 | | `python3.13-freethreading-debug` | Red Hat:hummingbird:1 | All versions | 0:3.13.15-1.4.hum1 | | `python3.13-idle` | Red Hat:hummingbird:1 | All versions | 0:3.13.15-1.4.hum1 | | `python3.13-libs` | Red Hat:hummingbird:1 | All versions | 0:3.13.15-1.4.hum1 | | `python3.13-test` | Red Hat:hummingbird:1 | All versions | 0:3.13.15-1.4.hum1 | ## How do I fix CVE-2026-19553? Upgrade libpython to a fixed version for your release line: 3.10.22, 3.11.17, 3.12.15 or 3.13.16. ## Is CVE-2026-19553 being exploited? There is no known exploitation of CVE-2026-19553 in the wild and no public exploit code. Public exploit code: - CPython - High - wrap_bio hostname skip (github_poc): https://github.com/abraxas/cve-2026-19553-wrap-bio ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-19553 and fix it if it is affected. What it is: CVE-2026-19553 is a high-severity vulnerability in CPython, published on 30 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link. Exploitation: There is no known exploitation of CVE-2026-19553 in the wild and no public exploit code. Affected packages and fixed versions: - libpython (Bitnami): affected all versions; fixed in 3.10.22, 3.11.17, 3.12.15, 3.13.16, 3.14.8 - python (Bitnami): affected all versions; fixed in 3.10.22, 3.11.17, 3.12.15, 3.13.16, 3.14.8 - python-min (Bitnami): affected all versions; fixed in 3.10.22, 3.11.17, 3.12.15, 3.13.16, 3.14.8 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-2026-19553/ (Markdown: https://insights.sbomify.com/CVE-2026-19553/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-19553 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-19553 - OSV: https://osv.dev/vulnerability/CVE-2026-19553 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-19553/ Summaries are generated and may contain mistakes; the official description above is the record.