CPU denial of service via zero packet size
Published Jul 21, 2026 · Updated Jul 21, 2026
Infinite loop in libssh on Red Hat Enterprise Linux and Hardened Images allows remote authenticated users to exhaust CPU. The channel-open handlers accept a peer-controlled maximum packet size of zero, store it in channel state, and pass it to channel_write_common(), whose remaining length never decreases. An authenticated SSH peer must send the zero value before a later channel write; the resulting infinite loop consumes CPU and interrupts the affected process.
Summary
What happened
Infinite loop in libssh on Red Hat Enterprise Linux and Hardened Images allows remote authenticated users to exhaust CPU. The channel-open handlers accept a peer-controlled maximum packet size of zero, store it in channel state, and pass it to channel_write_common(), whose remaining length never decreases. An authenticated SSH peer must send the zero value before a later channel write; the resulting infinite loop consumes CPU and interrupts the affected process.
The record
- CVE
- CVE-2026-59843
- Published
- Jul 21, 2026
- Updated
- Jul 21, 2026
- Vendor
- 389 Directory Server
- Product
- Red Hat Enterprise Linux 10
- Classifications
- CWE-400, CWE-835, T1499.004
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Jul 21, 2026CVE publishedPublication date reported by the CVE source.
- Jul 21, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Affected versions are unavailable in this record. Check the vendor advisory for version and patch details.
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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