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.
CVE-2026-63387
“—” beside the score: it is equal to the CVSS score beside it.
This high-severity CVE scores 7.0 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.4% (35th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.
Also known asEUVD-2026-63508 (ENISA EUVD)Source: ENISA EUVD
- CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
A fix is available — apply it.
- CVSS v3
- 7.0
- EG Score
- 7.0HIGHmedium confidence
- EG Risk
- 48EG Risk 48/100
EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.
How it’s computed (value × EchelonGraph’s weight)Severity70% × 45%Impact severity (EG Severity): CVSS 7.0 of 10. Never the KEV-floored or EPSS-lifted EG Score.Exploitation40% × 40%EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.Automatability0% × 15%CISA's SSVC Automatable value: no (Vulnrichment).SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Track* at high (mission-essential systems).Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.Action: A fix is available. Apply it within your standard update timelines. - EPSS PROB
- 0.4%
- EPSS %ILE
- 35th
- KEV
- Not listed
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (7.0): severity, escalated by confirmed exploitation. This CVE's 7.0 is its impact severity (EG Severity), not escalated.
- EG Severity
- 7.0 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.a secondary CVSS source · CVSS v3.0 or v3.1
- EG Likelihood
- 0.4% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-01). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
A fix is available. Apply it within your standard update timelines.
Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it
Published
August 20, 2026
Last Modified
October 26, 2026
Advisory Details (3)
Auto-updated Aug 20, 2026Libevent 2.2.2-alpha
Patch available: libevent/libevent release-2.2.2-alpha
https://github.com/libevent/libevent/releases/tag/release-2.2.2-alphaLibevent 2.1.13-stable
Patch available: libevent/libevent release-2.1.13-stable
https://github.com/libevent/libevent/releases/tag/release-2.1.13-stableOff-by-one stack buffer overflow in dnsname_to_labels via crafted DNS server response · Advisory · libevent/libevent · GitHub
https://github.com/libevent/libevent/security/advisories/GHSA-58rx-7448-jw47Vendor Advisories for CVE-2026-63387(13)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
- RHSA-2026:89197Red Hat Product SecurityCritical
Red Hat Security Advisory: OpenShift Container Platform 4.22.20 bug fix and security update
- RHSA-2026:72476Red Hat Product SecurityHigh
Red Hat Security Advisory: cert-manager Operator for Red Hat OpenShift 1.20.1
- RHSA-2026:72475Red Hat Product SecurityHigh
Red Hat Security Advisory: cert-manager Operator for Red Hat OpenShift 1.20.1
- RHSA-2026:72470Red Hat Product SecurityHigh
Red Hat Security Advisory: cert-manager Operator for Red Hat OpenShift 1.20.1
- RHSA-2026:72399Red Hat Product SecurityHigh
Red Hat Security Advisory: cert-manager Operator for Red Hat OpenShift 1.20.1
- RHSA-2026:72395Red Hat Product SecurityHigh
Red Hat Security Advisory: cert-manager Operator for Red Hat OpenShift 1.20.1
- RHSA-2026:72394Red Hat Product SecurityHigh
Red Hat Security Advisory: cert-manager Operator for Red Hat OpenShift 1.20.1
- RHSA-2026:71603Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat Update Infrastructure 5.3 security update
- +5 more
Patch Availability(13)
| Vendor / Ecosystem | Fix (by version range) / Patch | Released | Source |
|---|---|---|---|
| redhat | openshift/ose-rhel-coreos-9:4.22.9.8.202610241758-0 | 2026-10-27 | redhat |
| ubuntu | libevent-pthreads-2.1-7t64 (2.1.12-stable-9ubuntu2.2) @ noble | 2026-10-26 | ubuntu |
| redhat | cert-manager/jetstack-cert-manager-rhel9:1790589912 | 2026-09-28 | redhat |
| redhat | cert-manager/cert-manager-istio-csr-rhel9:1790589914 | 2026-09-28 | redhat |
| redhat | cert-manager/cert-manager-operator-rhel9:1790589855 | 2026-09-28 | redhat |
| redhat | cert-manager/cert-manager-istio-csr-rhel9:1790223719 | 2026-09-28 | redhat |
| redhat | cert-manager/cert-manager-operator-rhel9:1790272426 | 2026-09-28 | redhat |
| redhat | cert-manager/jetstack-cert-manager-rhel9:1790223279 | 2026-09-28 | redhat |
| redhat | rhui5/rhua-rhel9:1790242004 | 2026-09-24 | redhat |
| redhat | libevent-0:2.1.13-1.el9_8 | 2026-09-16 | redhat |
| redhat | libevent-0:2.1.8-11.el8_10 | 2026-09-16 | redhat |
| redhat | libevent-0:2.1.13-1.el10_2 | 2026-09-16 | redhat |
| redhat | libevent-main-2.1.13-0.1.hum1 | 2026-09-03 | redhat |
Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.
Affected Packages
(3 across 3 ecosystems)
Debian:12(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| libevent | 2.1.12-stable-8 |
| — |
Debian:13(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| libevent | 2.1.12-stable-10 |
| — |
Debian:14(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| libevent | 2.1.12-stable-10, 2.1.13-stable-1~deb13u1 |
| — |
Weakness Classification(3)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Additional Vendor Advisories
(1)
Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.
Data Freshness Timeline
(refreshed 9× in last 7d / 60× in last 30d)
Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.
Showing the most recent 97 of 180 refreshes on record for this CVE.
A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 3 repeat rows among the latest 100 are merged into the row they repeat. The 83 oldest rows on record are not shown and were not checked, so the counts can still include repeats.
- 2026-11-02 09:07 UTCEG score recompute
- 2026-11-02 09:07 UTCVendor advisory
- 2026-11-01 16:35 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-10-30 16:34 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-10-29 16:33 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-10-28 16:32 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-10-26 16:32 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-10-26 10:26 UTCEG score recompute
- 2026-10-26 10:26 UTCVendor advisory
- 2026-10-25 16:33 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-10-25 14:13 UTCEG score recompute
- 2026-10-24 16:33 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-23 16:32 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-22 16:35 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-21 16:33 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-20 10:44 UTCEG score recompute
- 2026-10-20 10:44 UTCVendor advisory
- 2026-10-19 16:32 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-18 16:32 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-18 03:23 UTCEG score recompute
- 2026-10-17 16:35 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-16 16:43 UTCEPSS rescoreEPSS 0.4% · 34th percentile
Show 72 moreShow fewer
- 2026-10-15 16:32 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-14 16:33 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-13 12:00 UTCEG score recompute
- 2026-10-13 12:00 UTCVendor advisory
- 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-12 15:49 UTCEG score recompute
- 2026-10-11 19:33 UTCEG score recompute
- 2026-10-11 16:48 UTCEG score recompute
- 2026-10-11 14:10 UTCEG score recompute
- 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-09 08:27 UTCEG score recompute
- 2026-10-09 08:27 UTCVendor advisory
- 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-08 05:21 UTCEG score recompute
- 2026-10-08 05:21 UTCVendor advisory
- 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-07 05:52 UTCVendor advisory
- 2026-10-06 16:53 UTCEG score recompute
- 2026-10-06 16:53 UTCVendor advisory
- 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-06 03:24 UTCVendor advisory
- 2026-10-06 03:24 UTCEG score recompute
- 2026-10-06 03:24 UTCVendor advisory
- 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-05 09:52 UTCEG score recompute
- 2026-10-05 09:52 UTCVendor advisory
- 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-04 20:52 UTCVendor advisory
- 2026-10-04 06:15 UTCVendor advisory
- 2026-10-03 17:16 UTCEG score recompute
- 2026-10-03 17:16 UTCVendor advisory
- 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-03 04:10 UTCEG score recompute
- 2026-10-03 04:10 UTCVendor advisory
- 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-02 14:50 UTCVendor advisory
- 2026-10-02 01:20 UTCEG score recompute
- 2026-10-02 01:20 UTCVendor advisory
- 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.4% · 36th percentile
- 2026-10-01 10:18 UTCVendor advisory
- 2026-09-30 21:18 UTCEG score recompute
- 2026-09-30 21:18 UTCVendor advisory
- 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.4% · 36th percentile
- 2026-09-30 08:13 UTCEG score recompute
- 2026-09-30 08:13 UTCVendor advisory
- 2026-09-28 21:38 UTCEG score recompute
- 2026-09-28 21:38 UTCVendor advisory
- 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.4% · 36th percentile
- 2026-09-28 05:00 UTCVendor advisory
- 2026-09-27 16:00 UTCEG score recompute
- 2026-09-27 16:00 UTCVendor advisory
- 2026-09-27 03:00 UTCEG score recompute
- 2026-09-27 03:00 UTCVendor advisory
- 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.4% · 36th percentile
- 2026-09-25 06:00 UTCVendor advisory
- 2026-09-24 17:00 UTCEG score recompute
- 2026-09-24 17:00 UTCVendor advisory
- 2026-09-24 04:00 UTCEG score recompute
- 2026-09-24 04:00 UTCVendor advisory
- 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-09-23 15:01 UTCVendor advisory
- 2026-09-23 02:00 UTCEG score recompute
- 2026-09-23 02:00 UTCVendor advisory
- 2026-09-22 13:01 UTCVendor advisory
- 2026-09-22 00:01 UTCEG score recompute
- 2026-09-22 00:01 UTCVendor advisory
- 2026-09-21 11:00 UTCVendor advisory
- 2026-09-20 22:00 UTCEG score recompute
- 2026-09-20 22:00 UTCVendor advisory
Related CVEs(same product + same vendor + same CWE)
Same product
10 shownDebian:12:libevent
Same vendor
10 shownredhat:RHSA-2026:63388 · redhat:RHSA-2026:67908 · redhat:RHSA-2026:67909
Frequently asked(5)
What is CVE-2026-63387?
When was the CVE record for CVE-2026-63387 published?
Is CVE-2026-63387 actively exploited?
What is the CVSS score of CVE-2026-63387?
How do I remediate CVE-2026-63387?
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-63387
Is Your Infrastructure Affected by CVE-2026-63387?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.