Exim: Use of Uninitialized Resource
CVE-2026-94056 is a high-severity use of uninitialized resource vulnerability in Exim, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 4.100.1 as the first without the flaw, so updating Exim to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.24% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Exim to 4.100.1 or a later version.
- Read the advisory on lists.exim.org for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
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.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- NoneNothing can be modified.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.5 | High | CNA (mitre.org) |
| CVSS 3.1 | 7.5 | High | NVD |
Official description
Exim before 4.100.1, when Proxy-Protocol is used with an attacker-controlled proxy, allows attackers to read certain uninitialized data from stack memory.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use of Uninitialized Resource
The product uses or accesses a resource that has not been initialized.
How developers prevent this class of flaw
- Explicitly initialize the resource before use. If this is performed through an API function or standard procedure, follow all required steps.
- Pay close attention to complex conditionals that affect initialization, since some branches might not perform the initialization.
- Avoid race conditions (CWE-362) during initialization routines.
More Use of Uninitialized Resource vulnerabilities (CWE-908)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Other vulnerabilities in Exim
- 7.8 High severity
- 9.8 Critical severity
- 9.1 Critical severity
- 9.8 Critical severity
- 7.5 High severity
- 9.8 Critical severity
Recent Use of Uninitialized Resource vulnerabilities
- 8.8 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.0 High severity
- 7.5 High severity
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