APT: UNIX Hard Link
CVE-2026-109518 is a high-severity UNIX hard link vulnerability in APT from Debian, with a CVSS 4.0 base score of 7.7 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. The record lists versions 1.2.36, 1.4.12, 1.6.19 as the first without the flaw, so updating APT to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.93% chance of exploitation within 30 days, higher than 61% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update APT to 1.2.36 or 1.4.12 or 1.6.19 or 1.8.2.4, whichever matches your release line, or a later version.
- Update APT to 1.0.1ubuntu2.24+esm4 or 1.2.36+esm1 or 1.6.19+esm1 or 2.0.12+esm1, whichever matches your release line, or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Debian | APT | before 1.2.36; 1.4.0 up to, but not including, 1.4.12; 1.6.0 up to, but not including, 1.6.19; 1.8.0 up to, but not including, 1.8.2.4; 1.8.3 through 1.8.5; 2.0.0 up to, but not including, 2.0.12; 2.2.0 up to, but not including, 2.2.5; 2.4.0 up to, but not including, 2.4.15; and 5 more ranges | 1.2.36, 1.4.12, 1.6.19, 1.8.2.4, 2.0.12, 2.2.5 |
| Ubuntu | APT | before 1.0.1ubuntu2.24+esm4; 1.2.0 up to, but not including, 1.2.36+esm1; 1.6.0 up to, but not including, 1.6.19+esm1; 2.0.0 up to, but not including, 2.0.12+esm1; 2.4.0 up to, but not including, 2.4.15ubuntu0.1; 2.8.0 up to, but not including, 2.8.4ubuntu0.1; 3.2.0 up to, but not including, 3.2.1ubuntu0.1; 3.3.0 up to, but not including, 3.3.3ubuntu0.1 | 1.0.1ubuntu2.24+esm4, 1.2.36+esm1, 1.6.19+esm1, 2.0.12+esm1, 2.4.15ubuntu0.1, 2.8.4ubuntu0.1 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Attack requirements
- PresentThe target must be in a specific state or configuration for the attack to work.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- PassiveA user only needs to do something routine, such as viewing a page.
- Confidentiality (vulnerable system)
- HighSerious loss of confidentiality on the vulnerable system.
- Integrity (vulnerable system)
- HighSerious loss of integrity on the vulnerable system.
- Availability (vulnerable system)
- HighSerious loss of availability on the vulnerable system.
- Confidentiality (other systems)
- NoneNo loss of confidentiality on systems beyond the vulnerable one.
- Integrity (other systems)
- NoneNo loss of integrity on systems beyond the vulnerable one.
- Availability (other systems)
- NoneNo loss of availability on systems beyond the vulnerable one.
Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. Scored by CNA (ubuntu.com).
Official description
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
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: UNIX Hard Link
The product, when opening a file or directory, does not sufficiently account for when the name is associated with a hard link to a target that is outside of the intended control sphere. This could allow an attacker to cause the product to operate on unauthorized files.
How developers prevent this class of flaw
- Follow the principle of least privilege when assigning access rights to entities in a software system. Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other references
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