# CVE-1999-0098: Sendmail buffer overflow in SMTP HELO command

Source: https://junglewise.ai/threats/cve-1999-0098-sendmail-buffer-overflow-in-smtp-helo-command  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 1998-04-01. Updated: 2026-05-10  
License: CC BY 4.0 with a link back

CVE-1999-0098 · Severity: critical · CVSS 10 · Published 1998-04-01

A critical vulnerability exists in Sendmail, a widely used mail transfer agent responsible for delivering email across the internet. By sending a specially crafted greeting command, a remote attacker can cause a system error that allows them to hide their activities or potentially gain full control over the mail server. This could lead to unauthorized access to sensitive communications, service disruption, or the use of the server for further malicious attacks.

Vendors: [Apple](https://junglewise.ai/threats/vendors/apple).

## Quick answers

**Is CVE-1999-0098 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-1999-0098 being exploited in the wild.

**How severe is CVE-1999-0098?** Critical severity, with a CVSS score of 10, published 1 April 1998.

**Which products and versions are affected?** Sendmail Sendmail.

**Is there a fix for CVE-1999-0098?** 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-1999-0098 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-1999-0098?** Check whether you run Appleshare or Pmail Mercury Mail Server. 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 buffer overflow vulnerability exists in the Sendmail SMTP service during the processing of the HELO command. The flaw is rooted in insufficient bounds checking when handling the hostname argument provided during the initial SMTP handshake. A remote, unauthenticated attacker can exploit this by sending an oversized or specially crafted HELO string over the network. Successful exploitation can lead to memory corruption, allowing the attacker to mask malicious activities or achieve full remote code execution with the privileges of the Sendmail process.

## Affected products

- Sendmail Sendmail

## Timeline

- 1998-04-01: disclosed: Initial publication date in NVD.

## References

- [https://exchange.xforce.ibmcloud.com/vulnerabilities/CVE-1999-0098](https://exchange.xforce.ibmcloud.com/vulnerabilities/CVE-1999-0098)