CVE-2026-18355 Memory corruption in Red Hat Directory Server 11.5 E4S for RHEL 8
Remote authenticated attackers can trigger a heap buffer overflow in 389 Directory Server via SASL integrity protection, leading to denial of service or code execution.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-18355?
CVE-2026-18355 is a high-severity memory corruption vulnerability in Red Hat Directory Server 11.5 E4S for RHEL 8, published on 7 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
A heap buffer overflow flaw was found in the SASL I/O layer of 389 Directory Server (389-ds-base). In sasl_io_start_packet(), the wrapped-record length read from the wire is validated only against an upper bound. A small wire length (0, 1, or 2) produces an encrypted_buffer_count below the already-consumed encrypted_buffer_offset, causing an unsigned subtraction underflow in sasl_io_read_packet(). PR_Recv is then requested to read approximately 4 GiB into a 1024-byte heap buffer, resulting in a heap buffer overflow with attacker-controlled content. After a successful SASL bind with integrity protection (SSF > 0), a remote authenticated attacker can cause a denial of service or potentially achieve remote code execution. This flaw is distinct from CVE-2026-11774, whose fix only guards against upper-bound overflow.
Weakness: CWE-191
Which versions are affected by CVE-2026-18355?
How do I fix CVE-2026-18355?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-18355 being exploited?
There is no known exploitation of CVE-2026-18355 in the wild and no public exploit code.
Sources
Also known as AZL-99980, DEBIAN-CVE-2026-18355, GHSA-r5vv-79fp-2427, UBUNTU-CVE-2026-18355.