Libressl: Double Free
CVE-2023-35784 is a critical-severity double free vulnerability in Libressl from OpenBSD, 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. The record lists versions 3.6.3, 3.7.3 as the first without the flaw, so updating Libressl to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.94% chance of exploitation within 30 days, higher than 61% of scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Libressl to 3.6.3 or 3.7.3, 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.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| OpenBSD | Libressl | before 3.6.3; 3.7.0 up to, but not including, 3.7.3 | 3.6.3, 3.7.3 |
| OpenBSD | Openbsd | 7.2; 7.3 | Not stated |
Version data comes from NVD's product matching. 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.
Official description
A double free or use after free could occur after SSL_clear in OpenBSD 7.2 before errata 026 and 7.3 before errata 004, and in LibreSSL before 3.6.3 and 3.7.x before 3.7.3. NOTE: OpenSSL is not affected.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Double Free
The product calls free() twice on the same memory address.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- Ensure that each allocation is freed only once. After freeing a chunk, set the pointer to NULL to ensure the pointer cannot be freed again. In complicated error conditions, be sure that clean-up routines respect the state of allocation properly. If the language is object oriented, ensure that object destructors delete each chunk of memory only once.
- Use a static analysis tool to find double free instances.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- ftp.openbsd.org/pub/OpenBSD/LibreSSL/libressl-3.6.3-relnotes.txtRelease Notes
- ftp.openbsd.org/pub/OpenBSD/LibreSSL/libressl-3.7.3-relnotes.txtRelease Notes
- ftp.openbsd.org/pub/OpenBSD/patches/7.2/common/026_ssl.patch.sig
- ftp.openbsd.org/pub/OpenBSD/patches/7.3/common/004_ssl.patch.sig
- github.com/libressl/openbsd/commit/e42d8f4b21a8a498e2eabbffe4c7b7d4ef7cec54
Recent Double Free vulnerabilities
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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