How severe is CVE-2021-29969?

CVE-2021-29969 has a CVSS 3.x base score of 5.9, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2021-29969 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (64th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-29969?

CVE-2021-29969 affects Mozilla Thunderbird. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-29969?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-29969 published?

CVE-2021-29969 was published on 2021-08-05 and last updated on 2026-06-17.

CVE-2021-29969

CVE-2021-29969 is a medium-severity vulnerability in Mozilla Thunderbird with a CVSS 3.x base score of 5.9. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-552.

Key facts

Severity: Medium (CVSS 3.x base score 5.9)
CVSS v2: 4.3
EPSS exploit prediction: 1% (64th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-552
Affected product: Mozilla Thunderbird
Published: 2021-08-05
Last modified: 2026-06-17

Description

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. This vulnerability affects Thunderbird < 78.12.

Frequently asked questions

What is CVE-2021-29969?: If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. This vulnerability affects Thunderbird < 78.12.
How severe is CVE-2021-29969?: CVE-2021-29969 has a CVSS 3.x base score of 5.9, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2021-29969 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (64th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-29969?: CVE-2021-29969 affects Mozilla Thunderbird. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-29969?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-29969 published?: CVE-2021-29969 was published on 2021-08-05 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*

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