CVE-2021-20314: Stack buffer overflow in libspf2 versions below 1.2.11 when processing certain SPF macros can lead to Denial o

Q: How do I fix CVE-2021-20314?

libspf2: upgrade to 1.2.11; enterprise linux: mitigate or apply the listed mitigation; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2021-20314 being exploited?

CVE-2021-20314 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-2021-20314 affect?

CVE-2021-20314 affects libspf2, enterprise linux, fedora. Severity is critical (CVSS 9.8). Stack buffer overflow in libspf2 versions below 1.2.11 when processing certain SPF macros can lead to Denial of service and potentially code execution via malicious crafted SPF explanation messages.

Q: How urgent is CVE-2021-20314?

Priority 66/100. Critical severity; Remotely exploitable, no login, no user action; On your watchlist

This week

CRITICAL 9.8REMOTEWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2021-20314 is a critical-severity flaw (CVSS 9.8) affecting libspf2, enterprise linux, fedora. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Stack buffer overflow in libspf2 versions below 1.2.11 when processing certain SPF macros can lead to Denial of service and potentially code execution via malicious crafted SPF explanation messages.

Why this priority

Critical severity
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.8% (top 13%)
CISA exploited list	No
Weakness	CWE-787
Published	2021-08-12
Last modified	2026-06-17

Publisher (CNA): Red Hat, Inc. · Vendor: fedoraproject · libspf2 · redhat

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-08-12 15:15 UTCPublished CVE record published
2026-06-17 03:33 UTCUpdated Record last modified

libspf2 libspf2 UPGRADE

Affected: < 1.2.11

Fixed in: 1.2.11

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy libspf2 || rpm -q libspf2 || libspf2 --version

2. UPGRADE to 1.2.11 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade libspf2

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade libspf2

Note

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

redhat enterprise linux MITIGATE

Affected: 7.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 7.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

fedoraproject fedora MITIGATE

Affected: 33 · 34 · 35

Fixed in: no fixed release known

Safe to downgrade to: a release before 33

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

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-2021-20314?

libspf2: upgrade to 1.2.11; enterprise linux: mitigate or apply the listed mitigation; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-20314 being exploited?

CVE-2021-20314 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-2021-20314 affect?

CVE-2021-20314 affects libspf2, enterprise linux, fedora. Severity is critical (CVSS 9.8). Stack buffer overflow in libspf2 versions below 1.2.11 when processing certain SPF macros can lead to Denial of service and potentially code execution via malicious crafted SPF explanation messages.

How urgent is CVE-2021-20314?

Priority 66/100. Critical severity; Remotely exploitable, no login, no user action; On your watchlist

Related CVEs

CVE-2023-42118 HIGH 8.8 MITIGATE Exim libspf2 Integer Underflow Remote Code Execution Vulnerability
CVE-2021-33913 CRITICAL 9.8 UPGRADE libspf2 before 1.2.11 has a heap-based buffer overflow that might allow remote attackers to execute arbitrary
CVE-2021-33912 CRITICAL 9.8 UPGRADE MITIGATE libspf2 before 1.2.11 has a four-byte heap-based buffer overflow that might allow remote attackers to execute

References

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