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CVE-2021-36386

25
FAUCET Score

CVE-2021-36386 is a denial-of-service vulnerability affecting Fetchmail versions prior to 6.4.20, specifically within the report_vbuild function, due to uninitialized vsnprintf va_list arguments. This flaw could allow malicious mail servers to trigger a denial of service or other unspecified impacts through crafted long error messages. With a CVSS score of 7.5 (HIGH), it is a network-exploitable vulnerability with low attack complexity, requiring no privileges or user interaction, leading to high availability impact. There is currently no evidence of active exploitation, no public exploit code available, and minimal community discussion or media coverage surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 6.4.20CPE matchmatch criteria
cpe:2.3:a:fetchmail:fetchmail:*:*:*:*:*:*:*:*
33CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
34CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
2.56%
Probability of exploitation in next 30 days
EPSS Percentile
83.5%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0256 is in the 71st percentile among its peer group of 51,506 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (3)

microsoftpatch availablevia msrc
Product: 19480-16823Fixed in: 6.4.22-1
microsoftpatch availablevia msrc
Product: cbl2 fetchmail 6.4.22-1 on CBL Mariner 2.0Fixed in: 6.4.22-1
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: fetchmail-0:6.4.24-1.el8
View patch

Vendor Advisories (2)

redhatCVE-2021-36386Moderate

fetchmail: DoS or information disclosure when logging long messages

Jul 28, 2021
microsoft2021-Jul/CVE-2021-36386Important

report_vbuild in report.c in Fetchmail before 6.4.20 sometimes omits initialization of the vsnprintf va_list argument which might allow mail servers to cause a denial of service or possibly have unspecified other impact via long error messages. NOTE: it is unclear whether use of Fetchmail on any realistic platform results in an impact beyond an inconvenience to the client user.

Jul 13, 2021

References

lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/AGYO5AHSXTCKA4NQC2Z4H3XMMYNAGC77
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/OIXKO6QW3AUHGJVWKJXBCOVBYJUJRBFC
security.gentoo.org / glsa/202209-14
Third Party Advisory
fetchmail.info / fetchmail-SA-2021-01.txt
Vendor Advisory
fetchmail.info / security.html
Vendor Advisory
openwall.com / lists/oss-security/2021/07/28/5
Mailing ListPatchThird Party Advisory
openwall.com / lists/oss-security/2021/08/09/1
Mailing List