CVE-2021-33912Public exploitNetwork attack vector

Heap corruption via signed-byte sprintf overflow

Published Jan 19, 2022 · Updated Aug 4, 2024

Heap buffer overflow in libspf2 before 1.2.11 allows remote attackers to corrupt memory via a crafted SPF DNS record and email sender. SPF_record_expand_data passes signed bytes from URL encoding to sprintf with a four-byte destination, causing values from 0x80 through 0xff to produce an eight-byte string and overwrite four adjacent heap bytes. Triggering requires control of the sender domain's SPF record and a non-ASCII sender byte; the corruption crashes the mail process or enables code execution when memory defenses are bypassed.

CVSS severity9.8
Critical
EPSS probability9.64%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap buffer overflow in libspf2 before 1.2.11 allows remote attackers to corrupt memory via a crafted SPF DNS record and email sender. SPF_record_expand_data passes signed bytes from URL encoding to sprintf with a four-byte destination, causing values from 0x80 through 0xff to produce an eight-byte string and overwrite four adjacent heap bytes. Triggering requires control of the sender domain's SPF record and a non-ASCII sender byte; the corruption crashes the mail process or enables code execution when memory defenses are bypassed.

The record

CVE
CVE-2021-33912
Published
Jan 19, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 19, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.3NIST NVDAV:N/AC:M/Au:N/C:C/I:C/A:C
9.8Canonical UbuntuCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8NIST NVDCVSS: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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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

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Your stack

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