CVE-2021-20314Public exploitNetwork attack vector

Remote code execution via SPF macro overflow

Published Aug 12, 2021 · Updated Feb 13, 2025

Stack buffer overflow in LibSPF2 before 1.2.11 allows remote attackers to execute code or crash mail services via crafted SPF records. SPF_record_compile_macro initializes ds_avail without subtracting the four-byte SPF_data header, so a long explanation macro overwrites four bytes beyond the stack buffer. Exploitation requires a mail server using the library to process SPF for an attacker-controlled domain; the demonstrated result is process termination, while code execution is also reported.

CVSS severity9.8
Critical
EPSS probability2.81%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Stack buffer overflow in LibSPF2 before 1.2.11 allows remote attackers to execute code or crash mail services via crafted SPF records. SPF_record_compile_macro initializes ds_avail without subtracting the four-byte SPF_data header, so a long explanation macro overwrites four bytes beyond the stack buffer. Exploitation requires a mail server using the library to process SPF for an attacker-controlled domain; the demonstrated result is process termination, while code execution is also reported.

The record

CVE
CVE-2021-20314
Published
Aug 12, 2021
Updated
Feb 13, 2025
Vendor
LibSPF2 Project
Product
LibSPF2
Classifications
CWE-787, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 12, 2021CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.2.11

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

LibSPF2 Project · LibSPF2version=1.2.11

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8UbuntuCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo