CVE-2020-12783Network attack vector

Authentication bypass via unchecked SPA response offsets

Published May 11, 2020 · Updated Aug 4, 2024

Out-of-bounds read in Exim 4.93 and earlier allows remote attackers to bypass SPA/NTLM authentication via a crafted response. The SPA decoder advances through the decoded response using attacker-controlled offsets without first ensuring that each resulting pointer remains within the response buffer. The affected authenticator is not enabled by default; when configured for an SMTP service, successful bypass grants the access controlled by that authenticator.

CVSS severity7.5
High
EPSS probability4.55%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in Exim 4.93 and earlier allows remote attackers to bypass SPA/NTLM authentication via a crafted response. The SPA decoder advances through the decoded response using attacker-controlled offsets without first ensuring that each resulting pointer remains within the response buffer. The affected authenticator is not enabled by default; when configured for an SMTP service, successful bypass grants the access controlled by that authenticator.

The record

CVE
CVE-2020-12783
Published
May 11, 2020
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-125, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 11, 2020CVE 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

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/A:N

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 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 exploitUnconfirmed

Weakness, pattern, technique

CWE-125Out-of-bounds Read
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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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