CVE-2019-16928: Exim Out-of-bounds Write Vulnerability

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 3 Mar 2022, 888 days after the CVE record was published.

How likely is exploitation in the next 30 days?

41.6%

EPSS score, percentile 98.7 of all scored records

How severe?

9.8 Critical

CVSS v3.1 base score, from CISA's enrichment of the record

What should I do?

CISA deadline 17 Mar 2022. Apply updates per vendor instructions.

Advisories and patches (6)

Which versions are affected?

Not stated. The CVE record gives vendor and product as “n/a” and the version as “unspecified”.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

What to do

CISA due date for this action: 17 March 2022.

Advisories and patches

• DSA-4536 (Vendor advisory)
• USN-4141-1 (Vendor advisory)
• FEDORA-2019-006dfc94cd (Vendor advisory)
• FEDORA-2019-e080507ba5 (Vendor advisory)
• FEDORA-2019-d778bd4137 (Vendor advisory)
• GLSA-202003-47 (Vendor advisory)

Linked from CISA's catalog entry

• https://nvd.nist.gov/vuln/detail/CVE-2019-16928

Affected products and versions

The CVE record does not name affected products or versions: vendor and product are “n/a” and the version is “unspecified”.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

About this vulnerability

Exim contains an out-of-bounds write vulnerability which can allow for remote code execution.

Summary: CISA's KEV catalog, as of 28 Oct 2026.

• CISA added CVE-2019-16928 to its Known Exploited Vulnerabilities (KEV) catalog on 3 Mar 2022.
• CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
• The due date CISA sets for the required action is 17 Mar 2022.
• The CVE record was published on 27 Sep 2019, 888 days before it was added to KEV.
• The CVE record carries a CVSS v3.1 base score of 9.8 (Critical), taken from CISA's enrichment of the record.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 41.6% (percentile 98.7), as of 28 Oct 2026.
• CISA's SSVC assessment in the CVE record: exploitation active, automatable yes, technical impact total.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.

Description

Exim 4.92 through 4.92.2 allows remote code execution, a different vulnerability than CVE-2019-15846. There is a heap-based buffer overflow in string_vformat in string.c involving a long EHLO command.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

Weakness

• CWE-787: Out-of-bounds Write

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.

Timeline

References

• lists.exim.org
• bugs.exim.org
• git.exim.org
• [oss-security] 20190928 Exim CVE-2019-16928 RCE using a heap-based buffer overflow
• [oss-security] 20190928 Re: Exim CVE-2019-16928 RCE using a heap-based buffer overflow
• [oss-security] 20190928 Re: Exim CVE-2019-16928 RCE using a heap-based buffer overflow

2 more in the CVE record.

More exploited Exim vulnerabilities

• CVE-2010-4344: Exim Heap-Based Buffer Overflow Vulnerability (added 25 Mar 2022)
• CVE-2010-4345: Exim Privilege Escalation Vulnerability (added 25 Mar 2022)
• CVE-2019-10149: Exim Mail Transfer Agent (MTA) Improper Input Validation (added 10 Jan 2022)
• CVE-2018-6789: Exim Buffer Overflow Vulnerability (added 3 Nov 2021)