Exim: Use After Free
CVE-2022-3620 is a critical-severity use after free vulnerability in Exim, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. There is no confirmed exploitation so far. EPSS estimates a 1.01% chance of exploitation within 30 days, higher than 64% of scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Check which version of Exim you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on git.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
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Exim | Exim | Not specified in the record | Not stated |
| Fedora Project | Fedora | 35; 36; 37 | Not stated |
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
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 5.6 | Medium | CNA (vuldb.com) |
| CVSS 3.1 | 9.8 | Critical | NVD |
Official description
A vulnerability was found in Exim and classified as problematic. This issue affects the function dmarc_dns_lookup of the file dmarc.c of the component DMARC Handler. The manipulation leads to use after free. The attack may be initiated remotely. The name of the patch is 12fb3842f81bcbd4a4519d5728f2d7e0e3ca1445. It is recommended to apply a patch to fix this issue. The associated identifier of this vulnerability is VDB-211919.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
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
Advisories
Third-party and government advisories
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/667V3ADXQ2MHUJMSXA3V…Third Party Advisory
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EIH4W5R7SHTUEQFWWKB4…Third Party Advisory
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XV2K2AWF62FSJ64B5CUZ…Third Party Advisory
- vuldb.com/?id.211919Third Party Advisory
Other vulnerabilities in Exim
- 7.5 High severity
- 7.8 High severity
- 9.8 Critical severity
- 9.1 Critical severity
- 9.8 Critical severity
- 7.5 High severity
Recent Use After Free vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 8.0 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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