CVE-2007-1558: The APOP protocol allows remote attackers to guess the first 3 characters of a password via man-in-the-middle

Routine

LOW 2.6MITIGATE

CVE-2007-1558 is a low-severity flaw (CVSS 2.6) affecting apop protocol. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The APOP protocol allows remote attackers to guess the first 3 characters of a password via man-in-the-middle (MITM) attacks that use crafted message IDs and MD5 collisions. NOTE: this design-level issue potentially affects all products that use APOP, including (1) Thunderbird 1.x before 1.5.0.12 and 2.x before 2.0.0.4, (2) Evolution, (3) mutt, (4) fetchmail before 6.3.8, (5) SeaMonkey 1.0.x before 1.0.9 and 1.1.x before 1.1.2, (6) Balsa 2.3.16

Why this priority

No elevated risk signals yet

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	2.6 (Low)
EPSS exploit chance	2.4% (top 16%)
CISA exploited list	No
Published	2007-04-16
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: apop protocol

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

Am I affected?

Timeline

2007-04-16 22:19 UTCPublished CVE record published
2026-06-16 22:37 UTCUpdated Record last modified

apop protocol apop protocol MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy apop-protocol || rpm -q apop-protocol || apop-protocol --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

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-2007-1558?

apop protocol: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2007-1558 being exploited?

CVE-2007-1558 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-2007-1558 affect?

CVE-2007-1558 affects apop protocol. Severity is low (CVSS 2.6). The APOP protocol allows remote attackers to guess the first 3 characters of a password via man-in-the-middle (MITM) attacks that use crafted message IDs and MD5 collisions. NOTE: this design-level issue potentially affects all products th

How urgent is CVE-2007-1558?

Priority 30/100. No elevated risk signals yet.

Software pages

Mozilla Thunderbird vulnerabilities

References

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