Rsyslog: rsyslog: denial of service via heap buffer overflow in rainerscript replace() function
Red Hat · Red Hat Enterprise Linux 10
7.5HighCVSS 3.1
Recommended action
Within 7 days
High technical severity; prioritise exposed affected systems while verifying vendor guidance.
Mitigation available
Distribution package intelligence
Ubuntu vendor package status
Canonical’s release and source-package findings are shown separately from local repository availability.
1 package state
Repository candidate not checked
A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.
Ubuntu release
Source package
Vendor state
Fixed version
Evidence
Ubuntu 24.04 LTSnoble · standard archive
rsyslog
Under evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.
Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.
1 current
CVE-2026-78002 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityrsyslog: rsyslog: Denial of service via heap buffer overflow in RainerScript replace() function
100 known affected
The vendor explicitly identifies these products as affected by this CVE.
rsyslog-crypto as a component of Red Hat Enterprise Linux 10
rsyslog-doc as a component of Red Hat Enterprise Linux 10
rsyslog-elasticsearch as a component of Red Hat Enterprise Linux 10
rsyslog-gnutls as a component of Red Hat Enterprise Linux 10
rsyslog-gssapi as a component of Red Hat Enterprise Linux 10
rsyslog-kafka as a component of Red Hat Enterprise Linux 10
rsyslog-mmaudit as a component of Red Hat Enterprise Linux 10
rsyslog-mmfields as a component of Red Hat Enterprise Linux 10
rsyslog-mmjsonparse as a component of Red Hat Enterprise Linux 10
rsyslog-mmkubernetes as a component of Red Hat Enterprise Linux 10
rsyslog-mmnormalize as a component of Red Hat Enterprise Linux 10
rsyslog-mmsnmptrapd as a component of Red Hat Enterprise Linux 10
Summary
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.
Remediation
To mitigate this vulnerability, restrict network access to the rsyslog service to only trusted hosts. This can be achieved by configuring firewall rules to limit incoming connections to UDP and TCP port 514. Alternatively, if remote syslog reception is not required, disable the `imudp` and `imtcp` modules in the `/etc/rsyslog.conf` configuration file. After modifying the rsyslog configuration or firewall rules, the rsyslog service or firewall service must be restarted for the changes to take effect.
Optional official sources
National CERT insights ?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.
Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.
Official European source
ENISA European Vulnerability Database
Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.
1 current
ENISA EUVD identifier
EUVD-2026-67085
No EUVD known-exploited evidence
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.
EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
7.5 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days
High technical severity; prioritise exposed affected systems while verifying vendor guidance.
Mitigation available
01
What, why and how
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
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.
Why
The product does not correctly calculate the size to be used when allocating a buffer, which could lead to a buffer overflow.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.
What
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.
Why
The product does not correctly calculate the size to be used when allocating a buffer, which could lead to a buffer overflow.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No confirmed evidence
No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.None recorded
No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.
Likely attack path
a network path → Incorrect Calculation of Buffer Size → disrupt the affected service
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness ?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-131: Incorrect Calculation of Buffer Size. The product does not correctly calculate the size to be used when allocating a buffer, which could lead to a buffer overflow.
CVSS vector ?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedDenial of serviceCWE-131
A
Official authority intelligence
Only matched European and national findings are included. Language selectors and unavailable sources are omitted.
ENISA EUVD · EUVD-2026-67085Official EUVD mapping
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.
Official EUVD record ↗BSI · German · WID-SEC-2026-3094rsyslog: Schwachstelle ermöglicht Denial of Service
Ein entfernter, anonymer Angreifer kann eine Schwachstelle in rsyslog ausnutzen, um einen Denial of Service Angriff durchzuführen.
Official advisory ↗Cyber Security Agency of Singapore · English · CSA-SB-20260902Security Bulletin 2 Sept 2026
The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 2 Sept 2026, published on 2 September 2026. Open the linked bulletin for the product, severity and reference information published in that issue.
Operational remediation based on structured source evidence.
Status ?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
No verified patch reference is present in the current structured sources. Check the vendor advisory before making a change.
Workaround
To mitigate this vulnerability, restrict network access to the rsyslog service to only trusted hosts. This can be achieved by configuring firewall rules to limit incoming connections to UDP and TCP port 514. Alternatively, if remote syslog reception is not required, disable the `imudp` and `imtcp` modules in the `/etc/rsyslog.conf` configuration file. After modifying the rsyslog configuration or firewall rules, the rsyslog service or firewall service must be restarted for the changes to take effect.
04
Evidence and provenance
Published 27 Aug 2026 · Last source change 29 Aug 2026, 22:06 UTC · CWE-131 · Incorrect Calculation of Buffer Size
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source ?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.FIRST · tracked since 2026-08-28
European sourceENISA EUVD · EUVD-2026-67085
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD awaiting enrichment
Core structured fields are present and their contributing authorities are shown above.
Affected versionsThe structured affected or fixed version information changed.
Before
rsyslog-crypto as a component of Red Hat Enterprise Linux 10; rsyslog-doc as a component of Red Hat Enterprise Linux 10; rsyslog-elasticsearch as a component of Red Hat Enterprise Linux 10; rsyslog-gnutls as a component of Red Hat Enterprise Linux 10; rsyslog-gssapi as a component of Red Hat Enterprise Linux 10; rsyslog-kafka as a component of Red Hat Enterprise Linux 10; rsyslog-mmaudit as a component of Red Hat Enterprise Linux 10; rsyslog-mmfields as a component of Red Hat Enterprise Linux 10; rsyslog-mmjsonparse as a component of Red Hat Enterprise Linux 10; rsyslog-mmkubernetes as a component of Red Hat Enterprise Linux 10; rsyslog-mmnormalize as a component of Red Hat Enterprise Linux 10; rsyslog-mmsnmptrapd as a component of Red Hat Enterprise Linux 10; rsyslog-mysql as a component of Red Hat Enterprise Linux 10; rsyslog-omamqp1 as a component of Red Hat Enterprise Linux 10; rsyslog-openssl as a component of Red Hat Enterprise Linux 10; rsyslog-pgsql as a component of Red Hat Enterprise Linux 10; rsyslog-relp as a component of Red Hat Enterprise Linux 10; rsyslog-snmp as a component of Red Hat Enterprise Linux 10; rsyslog-udpspoof as a component of Red Hat Enterprise Linux 10; rsyslog.src as a component of Red Hat Enterprise Linux 10; rsyslog as a component of Red Hat Enterprise Linux 6; rsyslog-gnutls as a component of Red Hat Enterprise Linux 6; rsyslog-gssapi as a component of Red Hat Enterprise Linux 6; rsyslog-mysql as a component of Red Hat Enterprise Linux 6; rsyslog-pgsql as a component of Red Hat Enterprise Linux 6; rsyslog-relp as a component of Red Hat Enterprise Linux 6; rsyslog-snmp as a component of Red Hat Enterprise Linux 6; rsyslog.src as a component of Red Hat Enterprise Linux 6; rsyslog7 as a component of Red Hat Enterprise Linux 6; rsyslog7-elasticsearch as a component of Red Hat Enterprise Linux 6; and 69 more
After
rsyslog-crypto as a component of Red Hat Enterprise Linux 10; rsyslog-doc as a component of Red Hat Enterprise Linux 10; rsyslog-elasticsearch as a component of Red Hat Enterprise Linux 10; rsyslog-gnutls as a component of Red Hat Enterprise Linux 10; rsyslog-gssapi as a component of Red Hat Enterprise Linux 10; rsyslog-kafka as a component of Red Hat Enterprise Linux 10; rsyslog-mmaudit as a component of Red Hat Enterprise Linux 10; rsyslog-mmfields as a component of Red Hat Enterprise Linux 10; rsyslog-mmjsonparse as a component of Red Hat Enterprise Linux 10; rsyslog-mmkubernetes as a component of Red Hat Enterprise Linux 10; rsyslog-mmnormalize as a component of Red Hat Enterprise Linux 10; rsyslog-mmsnmptrapd as a component of Red Hat Enterprise Linux 10; rsyslog-mysql as a component of Red Hat Enterprise Linux 10; rsyslog-omamqp1 as a component of Red Hat Enterprise Linux 10; rsyslog-openssl as a component of Red Hat Enterprise Linux 10; rsyslog-pgsql as a component of Red Hat Enterprise Linux 10; rsyslog-relp as a component of Red Hat Enterprise Linux 10; rsyslog-snmp as a component of Red Hat Enterprise Linux 10; rsyslog-udpspoof as a component of Red Hat Enterprise Linux 10; rsyslog.src as a component of Red Hat Enterprise Linux 10; rsyslog as a component of Red Hat Enterprise Linux 6; rsyslog-gnutls as a component of Red Hat Enterprise Linux 6; rsyslog-gssapi as a component of Red Hat Enterprise Linux 6; rsyslog-mysql as a component of Red Hat Enterprise Linux 6; rsyslog-pgsql as a component of Red Hat Enterprise Linux 6; rsyslog-relp as a component of Red Hat Enterprise Linux 6; rsyslog-snmp as a component of Red Hat Enterprise Linux 6; rsyslog.src as a component of Red Hat Enterprise Linux 6; rsyslog7 as a component of Red Hat Enterprise Linux 6; rsyslog7-elasticsearch as a component of Red Hat Enterprise Linux 6; and 70 more
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
CVE-2026-78002: Rsyslog: rsyslog: denial of service via heap buffer overflow in rainerscript replace() function | BlackTree
