CVE-2026-63387

HIGH

7.0

CVSS v3

Description

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent has an off-by-one stack buffer overflow in evdns.c when dnsname_to_labels formats a name-bearing DNS record at the end of the 64 KB stack buffer allocated by evdns_server_request_format_response. The final-label check permits j plus label_len plus one to equal buf_len, after which the terminating null byte is written to buf[buf_len]. A crafted DNS server response containing PTR, CNAME, MX, NS, or SOA data can trigger the one-byte out-of-bounds write and crash or corrupt the process. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

CWE-121Stack-based Buffer Overflow CWE-193 CWE-787Out-of-bounds Write

How to fix

Remediation Available

libeventDebian

Fixed in:2.1.13-stable-1CVE-2026-63387

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityHigh

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityLow

IntegrityLow

AvailabilityHigh

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

Exploit Intelligence

0.35%probability of exploitation in 30 days

28thpercentile

Low risk: more likely to be exploited than 28% of all known CVEs.

References

Other references3

Related Vulnerabilities

Other CWE-121 (Stack-based Buffer Overflow) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2025-22457	Critical	9.0	100%	KEV + Ransom	Fix
CVE-2025-0282	Critical	9.0	100%	KEV + Ransom	-
CVE-2021-20038	Critical	9.8	100%	KEV + Ransom	-
CVE-2009-0927	High	8.8	97%	KEV	Fix
CVE-2020-10924	High	8.8	87%	-	-
CVE-2022-20705	Critical	10.0	80%	-	-

Common questions

How do I fix CVE-2026-63387?

Upgrade libevent on debian unstable to 2.1.13-stable-1 or later.

Is CVE-2026-63387 being actively exploited?

Not that we know of. CVE-2026-63387 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.35% is the estimated probability that it will be exploited in the next 30 days. That is higher than 28% of all scored CVEs.

How severe is CVE-2026-63387?

CVE-2026-63387 has a CVSS v3 base score of 7.0, rated important. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2026-63387 affect?

Published advisories record a fix for libevent (Debian). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-08-20.