SB2026092971 - Ubuntu update for libevent
Published: September 29, 2026 Updated: September 30, 2026
Breakdown by Severity
- Low
- Medium
- High
- Critical
Description
This security bulletin contains information about 2 vulnerabilities.
1) Stack-based buffer overflow (CVE-ID: CVE-2026-63387)
CWE-ID: CWE-121 - Stack-based buffer overflow
CVSSv4: 8.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to cause a denial of service or corrupt adjacent stack state.
The vulnerability exists due to stack-based buffer overflow in dnsname_to_labels() in evdns.c when formatting DNS server responses containing name-bearing records. A remote attacker can send a specially crafted DNS query that causes the application to generate a crafted response to cause a denial of service or corrupt adjacent stack state.
The issue is triggered by an off-by-one condition when name encoding reaches the exact end of a 64 KB stack buffer before a terminating null byte is appended.
2) Out-of-bounds write (CVE-ID: CVE-2026-63388)
CWE-ID: CWE-787 - Out-of-bounds write
CVSSv4: 8.5 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to execute arbitrary code.
The vulnerability exists due to an out-of-bounds write in bufferevent_socket_set_conn_address_ when processing AF_UNIX accept() results for peer socket addresses. A remote attacker can connect to a vulnerable Unix domain socket with a specially crafted abstract-namespace address to execute arbitrary code.
On builds with NDEBUG, the assertion guarding the copy is disabled. Exploitation requires access to connect to the application's AF_UNIX listener, and on pthread-enabled servers the overwrite can corrupt a lock pointer that is later dereferenced inside libc.
Remediation
Install update from vendor's website.