CVE-2026-55556Public exploitNetwork attack vectorHinoki check available

Service crash via zero-byte Basic Auth allocation

Published Sep 18, 2026 · Updated Sep 18, 2026

Heap buffer overflow in rsyslog 8.2110.0 and later, before 8.2604.0, allows remote attackers to crash rsyslogd via an HTTP request. The imhttp parse_auth_header function passes attacker-sized decoded Basic credentials to apr_base64_decode after calloc(0, len) creates a zero-byte heap buffer. Exposure requires imhttp to be built, installed, loaded, and configured for Basic Authentication; a crafted request can stop log collection, while code execution is not demonstrated.

CVSS severity8.2
High
EPSS probability0.85%
Next 30 days · Oct 18, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Heap buffer overflow in rsyslog 8.2110.0 and later, before 8.2604.0, allows remote attackers to crash rsyslogd via an HTTP request. The imhttp parse_auth_header function passes attacker-sized decoded Basic credentials to apr_base64_decode after calloc(0, len) creates a zero-byte heap buffer. Exposure requires imhttp to be built, installed, loaded, and configured for Basic Authentication; a crafted request can stop log collection, while code execution is not demonstrated.

The record

CVE
CVE-2026-55556
Published
Sep 18, 2026
Updated
Sep 18, 2026
Vendor
rsyslog
Product
rsyslog
Classifications
CWE-122, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 18, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 18, 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=>= 8.2110.0, < 8.2604.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

rsyslog · rsyslogversion=>= 8.2110.0, < 8.2604.0

Published CVSS scores

8.2GitHubCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
5.9Amazon LinuxCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/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.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-122Heap-based Buffer Overflow
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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