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TI-2026-45187 Aliases CVE-2026-63387

Libevent: Off-by-one stack buffer overflow in dnsname_to_labels via crafted DNS server response

Priority MEDIUM 64CWE-121Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
High
Impact type
—
Confidentiality · integrity · availability
Low · Low · High
Fix status
Partial Red Hat: 10 fixed, 4 without a fix

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat.

Summary

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent has an off-by-one stack buffer overflow in evdns.c when dnsname_to_labels formats a name-bearing DNS record at the end of the 64 KB stack buffer allocated by evdns_server_request_format_response. The final-label check permits j plus label_len plus one to equal buf_len, after which the terminating null byte is written to buf[buf_len]. A crafted DNS server response containing PTR, CNAME, MX, NS, or SOA data can trigger the one-byte out-of-bounds write and crash or corrupt the process. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00416 36th percentileScored 2026-11-07
Fix Partial libevent (libevent): 2.2.2-alpha, 2.1.13Red Hat: 12 advisoriesRed Hat: 10 fixed, 4 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
libeventlibevent2.2.0-alpha to before 2.2.2-alpha; before 2.1.132.2.2-alpha, 2.1.13Patch availableCNA
  • libevent Vendorlibevent Affected 2.2.0-alpha to before 2.2.2-alpha; before 2.1.13 Fixed in 2.2.2-alpha, 2.1.13 Patch available CNA

Remediation

  • Fix · CNA libevent (libevent) Fixed in 2.2.2-alpha, 2.1.13

Red Hat 12 advisories

  • RHSA-2026:89197 Released 2026-10-27 · Red Hat rating Critical
    OpenShift Container Platform 4.22.20 bug fix and security update
    • Red Hat OpenShift Container Platform 4.22 rhcos-aarch64-4.22.9.8.202610241758-0, rhcos-ppc64le-4.22.9.8.202610241758-0, rhcos-s390x-4.22.9.8.202610241758-0 +1
  • RHSA-2026:72476 Released 2026-09-28 · Red Hat rating Important
    cert-manager Operator for Red Hat OpenShift 1.20.1
    • Cert Manager support for Red Hat OpenShift release 1.20 registry.redhat.io/cert-manager/cert-manager-operator-rhel9
  • RHSA-2026:72475 Released 2026-09-28 · Red Hat rating Important
    cert-manager Operator for Red Hat OpenShift 1.20.1
    • Cert Manager support for Red Hat OpenShift release 1.20 registry.redhat.io/cert-manager/cert-manager-istio-csr-rhel9
Show 9 more Red Hat advisories
  • RHSA-2026:72470 Released 2026-09-28 · Red Hat rating Important
    cert-manager Operator for Red Hat OpenShift 1.20.1
    • Cert Manager support for Red Hat OpenShift release 1.20 registry.redhat.io/cert-manager/jetstack-cert-manager-acmesolver-rhel9, registry.redhat.io/cert-manager/jetstack-cert-manager-rhel9
  • RHSA-2026:72399 Released 2026-09-28 · Red Hat rating Important
    cert-manager Operator for Red Hat OpenShift 1.20.1
    • Cert Manager support for Red Hat OpenShift release 1.20 registry.redhat.io/cert-manager/cert-manager-operator-rhel9
  • RHSA-2026:72395 Released 2026-09-28 · Red Hat rating Important
    cert-manager Operator for Red Hat OpenShift 1.20.1
    • Cert Manager support for Red Hat OpenShift release 1.20 registry.redhat.io/cert-manager/cert-manager-istio-csr-rhel9
  • RHSA-2026:72394 Released 2026-09-28 · Red Hat rating Important
    cert-manager Operator for Red Hat OpenShift 1.20.1
    • Cert Manager support for Red Hat OpenShift release 1.20 registry.redhat.io/cert-manager/jetstack-cert-manager-rhel9
  • RHSA-2026:71603 Released 2026-09-24 · Red Hat rating Important
    Red Hat Update Infrastructure 5.3 security update
    • Red Hat Update Infrastructure 5 registry.redhat.io/rhui5/cds-kubernetes-rhel9, registry.redhat.io/rhui5/cds-rhel9, registry.redhat.io/rhui5/haproxy-rhel9 +2
  • RHSA-2026:67910 Released 2026-09-16 · Red Hat rating Important
    libevent security update
    • Red Hat Enterprise Linux AppStream (v. 9) libevent-devel-2.1.13-1.el9_8, libevent-doc-2.1.13-1.el9_8
    • Red Hat Enterprise Linux BaseOS (v. 9) libevent-2.1.13-1.el9_8
  • RHSA-2026:67909 Released 2026-09-16 · Red Hat rating Important
    libevent security update
    • Red Hat Enterprise Linux AppStream (v. 10) libevent-devel-2.1.13-1.el10_2, libevent-doc-2.1.13-1.el10_2
    • Red Hat Enterprise Linux BaseOS (v. 10) libevent-2.1.13-1.el10_2
  • RHSA-2026:67908 Released 2026-09-16 · Red Hat rating Important
    libevent security update
    • Red Hat Enterprise Linux AppStream (v. 8) libevent-devel-2.1.8-11.el8_10
    • Red Hat Enterprise Linux BaseOS (v. 8) libevent-2.1.8-11.el8_10, libevent-doc-2.1.8-11.el8_10
  • RHSA-2026:63388 Released 2026-09-03 · Red Hat rating Important
    Red Hat Hardened Images RPMs Security Update
    • Red Hat Hardened Images libevent-2.1.13-0.1.hum1@aarch64, libevent-2.1.13-0.1.hum1@src, libevent-2.1.13-0.1.hum1@x86_64 +4

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat Enterprise Linux 6AffectedNo fix yet
Red Hat Enterprise Linux 7AffectedNo fix yet
Red Hat OpenShift Container Platform 4AffectedNo fix yet
Red Hat OpenShift Container Platform 5AffectedNo fix yet
Cert Manager support for Red Hat OpenShift release 1.20Fixed RHSA-2026:72394, RHSA-2026:72395, RHSA-2026:72399, RHSA-2026:72470, RHSA-2026:72475, RHSA-2026:72476
Red Hat Enterprise Linux AppStream (v. 10)Fixed RHSA-2026:67909
Red Hat Enterprise Linux AppStream (v. 8)Fixed RHSA-2026:67908
Red Hat Enterprise Linux AppStream (v. 9)Fixed RHSA-2026:67910
Red Hat Enterprise Linux BaseOS (v. 10)Fixed RHSA-2026:67909
Red Hat Enterprise Linux BaseOS (v. 8)Fixed RHSA-2026:67908
Red Hat Enterprise Linux BaseOS (v. 9)Fixed RHSA-2026:67910
Red Hat Hardened ImagesFixed RHSA-2026:63388
Red Hat OpenShift Container Platform 4.22Fixed RHSA-2026:89197
Red Hat Update Infrastructure 5Fixed RHSA-2026:71603
Not affected: 2 products
  • Cert Manager support for Red Hat OpenShift release 1.20
  • Red Hat OpenShift AI (RHOAI)

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-63387
  2. 2026-10-28 Fix available: Red Hat OpenShift Container Platform 4.22 · Red Hat
  3. 2026-10-29 Fix available: RHSA-2026:89197 · Red Hat
  4. 2026-10-30 Affected versions changed · Red Hat
  5. 2026-11-06 Affected versions changed · Red Hat

References

Other 3

  • TI-2026-45182 libevent evhttp: Multiple HTTP Parser Bugs Enable Request Smuggling CVSS 4.0CRITICAL 9.2
  • TI-2026-45184 Libevent: `evtag_unmarshal_header()` decodes a wire `uint32` length into a signed `int` return value. CVSS 4.0HIGH 8.7
  • TI-2026-45183 Libevent: decode_tag_internal() can lead to out-of-bounds read CVSS 4.0HIGH 8.7
  • TI-2026-45237 Libevent: Unbounded memory accumulation in WebSocket server via fragmented frames CVSS 3.1HIGH 7.5
  • TI-2026-45180 Libevent: Null Pointer Dereference in `evws_new_session` CVSS 4.0MEDIUM 5.7
  • TI-2026-45185 Libevent: HTTP header handling bugs create risk of access control bypass. CVSS 4.0CRITICAL 9.2
See all 9 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences