CVE-2026-55556

8.2 HIGH 0.9% exploit odds Fix listed Memory safety Library

What it is

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.

At a glance

Exploitability: Can be exploited over the network without logging in. High risk of service disruption.
Exploit odds: 0.9% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-06-16 23:11 UTC ReservedThe CVE id was reserved by its CNA
2026-09-18 17:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-09-24 21:22 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.9% in the next 30 days (EPSS).
Severity: 8.2 HIGH (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-09-18 17:16 UTC
Last modified: 2026-09-24 21:22 UTC
Exploit probability: 0.9% · EPSS, next 30 days
Weakness: CWE-122
Record status: Awaiting Analysis

Attack profile CVSS 4.0 · 8.2

Attack vector: Network
Complexity: Low
Attack requirements: Present
Privileges needed: None
User interaction: None
Confidentiality: None
Integrity: None
Availability: High

Raw vector

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

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-55556.md and follow it. Check whether this project is affected by CVE-2026-55556. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record