SB20260921136 - Red Hat Enterprise Linux 8 update for libevent
Published: September 21, 2026
Breakdown by Severity
- Low
- Medium
- High
- Critical
Description
This security bulletin contains information about 6 vulnerabilities.
1) Out-of-bounds read (CVE-ID: CVE-2026-63383)
CWE-ID: CWE-125 - Out-of-bounds read
CVSSv4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to an out-of-bounds read in decode_tag_internal() when parsing a malformed fragmented evbuffer tag. A remote attacker can send specially crafted input with more than 5 continuation bytes to cause a denial of service.
The issue is reachable through evtag_unmarshal_header(), and potential higher-level reachability exists via evrpc request parsing.
2) 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.
3) Integer overflow (CVE-ID: CVE-2026-63384)
CWE-ID: CWE-190 - Integer overflow
CVSSv4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to integer truncation in evtag_unmarshal_header() and evtag_unmarshal_string() when parsing crafted wire-encoded length fields. A remote attacker can send specially crafted input with a length value above INT_MAX to cause a denial of service.
The issue is triggered when a wire uint32 length is converted to a signed int, causing negative or truncated values that lead to an oversized wrapped allocation request in downstream string unmarshalling.
4) Input validation error (CVE-ID: CVE-2026-63382)
CWE-ID: CWE-20 - Improper input validation
CVSSv4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to smuggle HTTP requests and bypass access controls.
The vulnerability exists due to improper input validation in the evhttp HTTP parser when processing requests with multiple Transfer-Encoding headers. A remote attacker can send a specially crafted request with conflicting Transfer-Encoding headers to smuggle HTTP requests and bypass access controls.
Exploitation requires the service to be deployed behind an intermediary that interprets Transfer-Encoding differently and reuses the connection.
5) 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.
6) Inconsistent interpretation of HTTP requests (CVE-ID: CVE-2026-63385)
CWE-ID: CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling')
CVSSv4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to bypass access controls.
The vulnerability exists due to inconsistent interpretation of HTTP requests in evhttp_decode_uri_internal when processing percent-encoded URIs. A remote attacker can send a specially crafted request containing a %00 sequence to bypass access controls.
The issue arises because a decoded NUL byte can truncate the path for subsequent C string operations.
Remediation
Install update from vendor's website.