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# CVE-2024-6409: openssh
## Title
CVE-2024-6409: OpenSSH: Possible remote code execution in privsep child due to a race condition in signal handling
## Summary
As [discovered by Solar Designer (CIQ/Rocky Linux)](https://www.openwall.com/lists/oss-security/2024/07/08/2):
OpenSSH versions 8.7 and 8.8 and the corresponding portable releases call `cleanup_exit()` from `grace_alarm_handler()` when running in the privsep child process. `cleanup_exit()` was not meant to be called from a signal handler and may call other async-signal-unsafe functions. The current understanding is that in those upstream versions `cleanup_exit()` would not actually call async-signal-unsafe functions under those conditions, but with downstream distribution patches it sometimes does. Specifically, openssh-7.6p1-audit.patch found in Red Hat's package of OpenSSH adds code to `cleanup_exit()` that exposes the issue. Relevantly, this patch is found in EL 9, where the package is based on OpenSSH 8.7p1.
This is an EL9-specific issue similar to [CVE-2024-6387 regreSSHion](CVE-2024-6387.md).
Public disclosure date: July 8, 2024
## EL9
- Fixed in version: `8.7p1-38.1.el9_4.security.0.7` available July 8, 2024
## EL8
- Unaffected
## Mitigation
Set `LoginGraceTime 0` in `/etc/ssh/sshd_config` and do a `systemctl restart sshd`.
A drawback of this mitigation is that it will make the SSH server more susceptible to denial of service attacks.

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These are what we consider significant SIG/Security news items, not an exhaustive list of package updates and wiki edits.
## July 8, 2024
[openssh](packages/openssh.md) `8.7p1-38.1.el9_4.security.0.7` for EL9 adds a fix for [CVE-2024-6409](issues/CVE-2024-6409.md),
an EL9-specific issue similar to [CVE-2024-6387 regreSSHion](issues/CVE-2024-6387.md).
## July 1, 2024
[openssh](packages/openssh.md) `8.7p1-38.el9_4.security.0.5` for EL9 adds a fix for [CVE-2024-6387 regreSSHion](issues/CVE-2024-6387.md).

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## EL9
- Version `8.7p1-38.el9_4.security.0.5`
- Based on `8.7p1-38.el9`
- Version `8.7p1-38.1.el9_4.security.0.7`
- Based on `8.7p1-38.el9_4.1`
### Changes summary
- Instead of linking against `libsystemd`, load it dynamically in a temporary child process to avoid polluting actual `sshd`'s address space with that library and its many dependencies (shortens `ldd sshd` output from 28 to 20 lines)
- Build without Kerberos support (further shortens `ldd sshd` from 20 to 13 lines)
- Fix CVE-2024-6387 regreSSHion
- Fix [CVE-2024-6409](../issues/CVE-2024-6409.md)
### Change log
```
* Mon Jul 08 2024 Solar Designer <solar@openwall.com> 8.7p1-38.1.el9_4.security.0.7
- Fix CVE-2024-6409
* Mon Jul 08 2024 Solar Designer <solar@openwall.com> 8.7p1-38.1.el9_4.security.0.6
- Rebase on 8.7p1-38.1
* Mon Jul 01 2024 Solar Designer <solar@openwall.com> 8.7p1-38.el9_4.security.0.5
- Fix CVE-2024-6387 regreSSHion