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Fencer Intel
high 8.2

CVE-2026-55556 json

Rsyslog: Heap buffer overflow in imhttp plugin Basic Authentication handling

published 4mo ago modified last mo. also EUVD-2026-83184 , GHSA-947w-69ph-mc2r

Unreviewed: the maintainers' own advisory

Published by the maintainers on their GitHub repository rsyslog/rsyslog. GitHub has not reviewed it into the GitHub Advisory Database, so the affected packages and versions are the maintainers' word. Read the full advisory on GitHub.

cvss
8.2
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.9%
EPSS 0.9% chance of exploitation in 30 days, percentile 58%
public exploits
0
none known

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.

Patch / fix

  • rsyslog rsyslog 8.2604.0
  • rsyslog Debian 14 8.2604.0-1

debian advisories DEBIAN-CVE-2026-55556

  • rsyslog Alpine 3.24 8.2608.0-r0

alpine advisories ALPINE-CVE-2026-55556

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Is CVE-2026-55556 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-55556 updated cvss 7.5

rsyslog: Rsyslog: Denial of Service via heap buffer overflow in imhttp module

  • Red Hat Enterprise Linux 6 rsyslog, rsyslog7, rsyslog-relp, rsyslog-snmp, rsyslog-mysql, rsyslog-pgsql, +9 more Red Hat Enterprise Linux 7 rsyslog, rsyslog-relp, rsyslog-snmp, rsyslog-kafka, rsyslog-mysql, rsyslog-pgsql, +11 more Red Hat Enterprise Linux 8 rsyslog, rsyslog-relp, rsyslog-snmp, rsyslog-kafka, rsyslog-mysql, rsyslog-pgsql, +13 more Red Hat Enterprise Linux 9 rsyslog, rsyslog-relp, rsyslog-snmp, rsyslog-kafka, rsyslog-mysql, rsyslog-pgsql, +14 more Red Hat Enterprise Linux 10 rsyslog
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
last mo.

Exploit prediction

0.85% chance of exploitation in the next 30 days, higher than 58% of all scored CVEs (FIRST EPSS, 2026-11-11).

Exploits and checks

  • github.com https://github.com/rsyslog/rsyslog/security/advisories/GHSA-947w-69ph-mc2r referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 8.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CNA 4.0 8.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

  • rsyslog rsyslog

Classification

Weakness
  • CWE-122 Heap-based Buffer Overflow

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of rsyslog/rsyslog published their own advisory on GitHub. Reviewed sources take precedence over it.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.