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TI-2026-40100 Aliases CVE-2026-55556

Rsyslog: Heap buffer overflow in imhttp plugin Basic Authentication handling

Priority HIGH 75CWE-122Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
Present
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-122 and the CVSS impact.

Summary

Rsyslog is a rocket-fast system for log processing. From 8.2110.0 until 8.2604.0, the optional imhttp module's parse_auth_header function in contrib/imhttp/imhttp.c allocates a zero-byte heap buffer with calloc(0, len) when an HTTP Basic Authorization value exceeds its fixed work buffer, then passes that pointer to apr_base64_decode. An unauthenticated remote attacker can send an oversized encoded credential to an imhttp endpoint configured for Basic Authentication, causing decoded data to overwrite adjacent heap memory before credential validation. Deployments that do not install, load, and use imhttp with Basic Authentication are not affected. The demonstrated impact is a process crash that interrupts log collection, and code execution has not been demonstrated. This issue is fixed in version 8.2604.0.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00853 58th percentileScored 2026-11-07
Fix Fixed rsyslog (rsyslog): 8.2604.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
rsyslogrsyslog8.2110.0 to before 8.2604.08.2604.0Patch availableCNA
  • rsyslog Vendorrsyslog Affected 8.2110.0 to before 8.2604.0 Fixed in 8.2604.0 Patch available CNA

Remediation

  • Fix · CNA rsyslog (rsyslog) Fixed in 8.2604.0

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

Not affected: 5 products
  • Red Hat Enterprise Linux 10
  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 7
  • Red Hat Enterprise Linux 8
  • Red Hat Enterprise Linux 9

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-55556

References

Other 4

  • TI-2018-15792 rsyslog librelp version 1.2.14 and earlier contains a Buffer Overflow vulnerability in… CVSS 3.0CRITICAL 9.8
  • TI-2019-12711 An issue was discovered in Rsyslog v8.1908.0. CVSS 3.1CRITICAL 9.8
  • TI-2019-12712 An issue was discovered in Rsyslog v8.1908.0. CVSS 3.1CRITICAL 9.8
  • TI-2019-12710 contrib/pmdb2diag/pmdb2diag.c in Rsyslog v8.1908.0 allows out-of-bounds access because the level length is mishandled. CVSS 3.1CRITICAL 9.8
  • TI-2017-09315 The zmq3 input and output modules in rsyslog before 8.28.0 interpreted description fields… CVSS 3.0CRITICAL 9.8
  • TI-2022-08713 Buffer overflow in TCP syslog server (receiver) components in rsyslog CVSS 3.1HIGH 8.1
See all 22 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences