CVE-2005-0021: Multiple buffer overflows in Exim before 4.43 may allow attackers to execute arbitrary code via (1) an IPv6 ad

Q: How do I fix CVE-2005-0021?

exim: upgrade to newer than 4.40. Exact commands for each OS are on this page.

Q: Is CVE-2005-0021 being exploited?

CVE-2005-0021 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2005-0021 affect?

CVE-2005-0021 affects exim. Severity is high (CVSS 7.2). Multiple buffer overflows in Exim before 4.43 may allow attackers to execute arbitrary code via (1) an IPv6 address with more than 8 components, as demonstrated using the -be command line option, which triggers an overflow in the host_aton

Q: How urgent is CVE-2005-0021?

Priority 52/100. High severity; Public exploit reference

This month

HIGH 7.2UPGRADE

CVE-2005-0021 is a high-severity flaw (CVSS 7.2) affecting exim. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Multiple buffer overflows in Exim before 4.43 may allow attackers to execute arbitrary code via (1) an IPv6 address with more than 8 components, as demonstrated using the -be command line option, which triggers an overflow in the host_aton function, or (2) the -bh command line option or dnsdb PTR lookup, which triggers an overflow in the dns_build_reverse function.

Why this priority

High severity
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	7.2 (High)
EPSS exploit chance	2.6% (top 15%)
CISA exploited list	No
Published	2005-05-02
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: university of cambridge

Last updated 2026-06-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2005-05-02 04:00 UTCPublished CVE record published
2026-06-16 22:10 UTCUpdated Record last modified

university of cambridge exim UPGRADE

Affected: <= 4.40 · 4.41 · 4.42

Fixed in: newer than 4.40

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy exim || rpm -q exim || exim --version

2. UPGRADE to newer than 4.40 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade exim

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade exim

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Exploit-DB: Exim 4.41 - 'dns_build_reverse' Local Buffer Overflow
Exploit-DB: Exim 4.41 - 'dns_build_reverse' Local Read Emails

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2005-0021?

exim: upgrade to newer than 4.40. Exact commands for each OS are on this page.

Is CVE-2005-0021 being exploited?

CVE-2005-0021 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2005-0021 affect?

CVE-2005-0021 affects exim. Severity is high (CVSS 7.2). Multiple buffer overflows in Exim before 4.43 may allow attackers to execute arbitrary code via (1) an IPv6 address with more than 8 components, as demonstrated using the -be command line option, which triggers an overflow in the host_aton

How urgent is CVE-2005-0021?

Priority 52/100. High severity; Public exploit reference

Software pages

Exim vulnerabilities

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References

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