Bug 2521135 (CVE-2026-78002)

Summary: CVE-2026-78002 rsyslog: rsyslog: Denial of service via heap buffer overflow in RainerScript replace() function
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: rhel-process-autobot, security-response-team, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Doc Text:
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.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 2524995    
Bug Blocks:    
Deadline: 2026-08-24   

Description OSIDB Bzimport 2026-08-21 19:43:38 UTC 
doFuncReplace() in grammar/rainerscript.c implements replace(source, find, replaceWith) as two passes over the source string: pass 1 computes the output length, pass 2 allocates that many bytes with
es_newStr() and fills them. On partial-match failure the two passes rewind by different amounts — pass 1 does i -= (j - 1), pass 2 does i -= j — so pass 1 resumes scanning at matchStart + 2 while pass 2 resumes at matchStart + 1. Every match that begins one byte after a failed partial match is therefore counted by pass 2 but not by pass 1. When replaceWith is longer than find, each such match makes the allocation short by lReplaceWith - lfind bytes, and pass 2 writes past the end of the buffer. Neither store site is bounds-checked. The source string is normally a message property ($msg, $rawmsg, …), so an unauthenticated remote syslog sender chooses the number of missed matches and thus the size of the overflow.