CVE-2026-115559Python Software Foundation CPython vulnerability
CVE-2026-115559 is a vulnerability in Python Software Foundation CPython, rated medium (6.3 on CVSS 4.0).
Why this priority: Medium severity, with no exploitation signal.
Published · Updated · NVD status: Awaiting Analysis
What it is
The record does not classify the weakness yet; the description below says what the reporter found.
How it is reached
An attacker can exploit it over the network, without an account, and nobody has to click anything. Success also depends on conditions the attacker does not fully control.
What an attacker gains
The direct impact is limited: partial access to data or a partial outage.
Is it being exploited?
There is no public report of exploitation yet.
What to do
- Upgrade Python Software Foundation CPython to 3.16.0 or later.
- Until it is patched, keep it off the internet or behind a VPN, allowlist or authenticating proxy.
Description from NVD
IMAP4.starttls() wraps the socket in TLS but leaves self._readbuf, imaplib's own read-ahead buffer, untouched. Any plaintext bytes that arrived in the same recv() as the tagged OK to STARTTLS are returned by readline() after the handshake, so the client treats them as the first responses on the protected channel. A network attacker who cannot break TLS can append forged lines after the server's OK, let the handshake complete with the real server and a valid certificate, and have the client accept the forged CAPABILITY and the forged tagged completion of the next command. This is the STARTTLS command/response injection class of CVE-2011-0411.
What this means for your architecture.
A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.
Components it touches
- Python Software Foundation CPython. Start from where it runs and what it is connected to.
Trust boundaries in play
- Internet-facing entry points. No account is needed. Any instance reachable from outside your perimeter, through a load balancer, gateway, VPN or exposed admin port, is in scope.
Questions to answer about your own systems
- Where does Python Software Foundation CPython run in your systems, and at which version?
- Which of those instances can be reached from the internet or partner networks?
- What can it reach once compromised: which data stores, secrets and services?
Read more
Patches and commits
Issue reports
Sources
- CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
- Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
- Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
- Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.