CVE-2023-3603: Processing sftp server read may cause null dereference

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-07-21 · updated 2026-06-17
Weakness: CWE-476

Description

A missing allocation check in sftp server processing read requests may cause a NULL dereference on low-memory conditions. The malicious client can request up to 4GB SFTP reads, causing allocation of up to 4GB buffers, which was not being checked for failure. This will likely crash the authenticated user's sftp server connection (if implemented as forking as recommended). For thread-based servers, this might also cause DoS for legitimate users. Given this code is not in any released versions, no security releases have been issued.

Affected products

libssh: before 0.8.9 — fixed in 0.8.9

How to fix

Upgrade to a fixed version: libssh 0.8.9. Check the vendor advisory for mitigations.

References

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