CVE-2026-109518Debian APT time-of-check to time-of-use race
CVE-2026-109518 is a time-of-check to time-of-use race in Debian APT, rated high (7.7 on CVSS 4.0).
Why this priority: High severity, with no exploitation signal yet.
Published · Updated · NVD status: Received
What it is
Something is checked, then changed by an attacker before it is used.
How it is reached
An attacker can exploit it over the network, without an account, but someone has to act first, such as opening a file or following a link. Success also depends on conditions the attacker does not fully control.
What an attacker gains
A successful attack can read the data it protects, change data or behaviour and take it offline. In practice, this kind of flaw lets an attacker win a timing window to bypass a check or corrupt shared state.
Is it being exploited?
There is no public report of exploitation yet. EPSS estimates a 0.93% chance of exploitation activity in the next 30 days, higher than 61% of scored CVEs.
What to do
- Apply the update for your edition of Debian APT. Fixed builds: APT: 1.2.36, 1.4.12, 1.6.19; APT: 1.0.1ubuntu2.24+esm4, 1.2.36+esm1, 1.6.19+esm1.
- Until it is patched, keep it off the internet or behind a VPN, allowlist or authenticating proxy.
- Warn the people who use it, and filter files and links on the way in.
Description from NVD
On Debian, Ubuntu, and derivative Linux distributions, an on-path attacker who can manipulate the HTTP traffic (including a malicious mirror or proxy) between an APT client and an archive server triggered by a package install can trick the client into installing an attacker-controlled unverified package and achieve remote code execution with root privileges.
The vulnerability is caused by the reuse of hard links and requires the client to follow redirects and retry the download of package files. It requires the client to have a non-zero Acquire::Retries configuration setting; the value 3 is the default starting with Debian 12 (bookworm) and Ubuntu 22.04 LTS (Jammy Jellyfish), so older releases are unaffected in a default configuration
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
- Request handlers and jobs that share state. The flaw sits between concurrent requests or processes.
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.
- People who open files and links. Mail, chat and browsers are the delivery path.
- Between concurrent requests or processes. An attacker who crosses it can win a timing window to bypass a check or corrupt shared state.
Questions to answer about your own systems
- Where does Debian APT 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?
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.