Quick answers
- Is CVE-2026-59843 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-59843 being exploited in the wild.
- How severe is CVE-2026-59843?
- Medium severity, with a CVSS score of 6.5, published 21 July 2026.
- Which products and versions are affected?
- Libssh unspecified; Red Hat Enterprise Linux 10 affected; Red Hat Enterprise Linux 8 affected; Red Hat Enterprise Linux 9 affected.
- Is there a fix for CVE-2026-59843?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-59843 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-59843?
- Check whether you run Libssh, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8 or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
A vulnerability exists in the channel handling logic of libssh, specifically within ssh_packet_channel_open() and ssh_packet_channel_open_conf(). The implementation fails to validate the maximum packet size advertised by a peer, allowing a value of zero to be accepted and stored in the channel state. When channel_write_common() is subsequently called, the zero value prevents the remaining data length from being decremented, resulting in an infinite loop. An authenticated attacker can trigger this by sending an SSH_MSG_CHANNEL_OPEN or SSH_MSG_CHANNEL_OPEN_CONFIRMATION message with a zero packet size, leading to uncontrolled resource consumption (CPU) and denial of service.
Affected products
- libssh libssh unspecified
- Red Hat Red Hat Enterprise Linux 8 affected
- Red Hat Red Hat Enterprise Linux 9 affected
- Red Hat Red Hat Enterprise Linux 10 affected
- Red Hat Red Hat Hardened Images affected
Timeline
- 2026-07-08: disclosed: Initial report in Red Hat Bugzilla
- 2026-07-21: advisory: NVD publication date