# 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.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 Sep 2026
- **Updated:** 8 Oct 2026
- **Also known as:** AZL-99980, DEBIAN-CVE-2026-18355, GHSA-r5vv-79fp-2427, UBUNTU-CVE-2026-18355

## 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 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2026-18355?


## How do I fix CVE-2026-18355?

Apply the vendor's patch.

## Is CVE-2026-18355 being exploited?

There is no known exploitation of CVE-2026-18355 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18355 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-18355 in the wild and no public exploit code.

Affected product: Red Hat Directory Server 11.5 E4S for RHEL 8. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-18355/ (Markdown: https://insights.sbomify.com/CVE-2026-18355/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18355
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18355
- OSV: https://osv.dev/vulnerability/CVE-2026-18355

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-18355/
Summaries are generated and may contain mistakes; the official description above is the record.