Exim before 4.99.3, in certain GnuTLS configurations, has a remotely reachable use-after-free in the BDAT body parsing path. It is triggered when a client sends a TLS close_notify mid-body during a CHUNKING transfer, followed by a final cleartext byte on the same TCP connection. This can lead to heap corruption. An unauthenticated network attacker exploiting this vulnerability could execute arbitrary code.
Weakness
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 Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Exim | Exim | 4.97 (including) | 4.99.3 (excluding) |
| Exim4 | Ubuntu | devel | * |
| Exim4 | Ubuntu | esm-infra-legacy/trusty | * |
| Exim4 | Ubuntu | esm-infra-legacy/xenial | * |
| Exim4 | Ubuntu | esm-infra/bionic | * |
| Exim4 | Ubuntu | esm-infra/focal | * |
| Exim4 | Ubuntu | esm-infra/xenial | * |
| Exim4 | Ubuntu | jammy | * |
| Exim4 | Ubuntu | noble | * |
| Exim4 | Ubuntu | questing | * |
| Exim4 | Ubuntu | resolute | * |
Potential Mitigations
References
- https://code.exim.org/exim/wiki/wiki/EximSecurity
- https://exim.org
- https://exim.org/static/doc/security/CVE-2026-45185.txt
- https://exim.org/static/doc/security/EXIM-Security-2026-05-01.1/
- https://news.ycombinator.com/item?id=48111748
- https://www.openwall.com/lists/oss-security/2026/05/12/4
- https://xbow.com/blog/dead-letter-cve-2026-45185-xbow-found-rce-exim
- http://www.openwall.com/lists/oss-security/2026/05/12/25