CVE-2026-63387Public exploitNetwork attack vector

Process corruption via off-by-one DNS response write

Published Aug 20, 2026 · Updated Aug 25, 2026

Stack buffer overflow in Libevent before 2.1.13 and 2.2.0-alpha through 2.2.1-alpha allows remote attackers to crash or corrupt processes. In evdns.c, dnsname_to_labels permits the final label to end exactly at the 64 KB response buffer boundary, then writes a null byte to buf[buf_len]. Exposure requires an application to use the evdns_server family APIs for name-bearing PTR, CNAME, MX, NS, or SOA records; the one-byte overwrite can terminate the process or corrupt adjacent stack state.

CVSS severity7.0
High
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack buffer overflow in Libevent before 2.1.13 and 2.2.0-alpha through 2.2.1-alpha allows remote attackers to crash or corrupt processes. In evdns.c, dnsname_to_labels permits the final label to end exactly at the 64 KB response buffer boundary, then writes a null byte to buf[buf_len]. Exposure requires an application to use the evdns_server family APIs for name-bearing PTR, CNAME, MX, NS, or SOA records; the one-byte overwrite can terminate the process or corrupt adjacent stack state.

The record

CVE
CVE-2026-63387
Published
Aug 20, 2026
Updated
Aug 25, 2026
Vendor
Libevent
Product
Libevent
Classifications
CWE-787, CWE-121, CWE-193, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.1.13
  2. Affected versionversion=>= 2.2.0-alpha, < 2.2.2-alpha

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Libevent · Libeventversion=< 2.1.13; version=>= 2.2.0-alpha, < 2.2.2-alpha

Published CVSS scores

7.0GitHubCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H

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 exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
CWE-121Stack-based Buffer Overflow
CWE-193Off-by-one Error
T1499.004Application or System Exploitation

Public exploit references

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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