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NVD / CVE Program· CNA GitHub_M

CVE-2026-63383: Libevent: decode_tag_internal() can lead to out-of-bounds read

HighCVSS 8.7 · v4.0—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 34/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.48% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • Fixed version: libevent (AlmaLinux:10) 2.1.13-1.el10_2; libevent-devel (AlmaLinux:10) 2.1.13-1.el10_2; libevent-doc (AlmaLinux:10) 2.1.13-1.el10_2.

Low priority for now. Upgrade to libevent (AlmaLinux:10) 2.1.13-1.el10_2; libevent-devel (AlmaLinux:10) 2.1.13-1.el10_2; libevent-doc (AlmaLinux:10) 2.1.13-1.el10_2 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent can read beyond a contiguous evbuffer region in event_tagging.c when decode_tag_internal requests at most five bytes from evbuffer_pullup but iterates using the full logical buffer length. A fragmented evbuffer containing a six-byte malformed tag can therefore advance past the pullup window and trigger an out-of-bounds read, which can crash a process that decodes attacker-controlled tagged RPC data. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

Published
Aug 20, 2026
Updated
Oct 26, 2026
EPSS
0.4% · 42th percentile

Report tools

JSON

Action score

34

Monitor

Low priority for now.

CVSS
34 / 40 · 8.7 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.4%

CISA SSVC decision

Exploitation
proof of concept
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · GitHub_M
8.7
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

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Follow CVE-2026-63383

When you'll hear from us

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  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

  • libevent libevent

    • >= 2.2.0-alpha, < 2.2.2-alpha, < 2.1.13affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:10libeventbefore 2.1.13-1.el10_22.1.13-1.el10_2
AlmaLinux:10libevent-develbefore 2.1.13-1.el10_22.1.13-1.el10_2
AlmaLinux:10libevent-docbefore 2.1.13-1.el10_22.1.13-1.el10_2
AlmaLinux:8libeventbefore 2.1.8-11.el8_102.1.8-11.el8_10
AlmaLinux:8libevent-develbefore 2.1.8-11.el8_102.1.8-11.el8_10
AlmaLinux:8libevent-docbefore 2.1.8-11.el8_102.1.8-11.el8_10
AlmaLinux:9libeventbefore 2.1.13-1.el9_82.1.13-1.el9_8
AlmaLinux:9libevent-develbefore 2.1.13-1.el9_82.1.13-1.el9_8
AlmaLinux:9libevent-docbefore 2.1.13-1.el9_82.1.13-1.el9_8
Debian:12libeventbefore 2.1.12-stable-8+deb12u12.1.12-stable-8+deb12u1
Debian:13libeventbefore 2.1.13-stable-1~deb13u12.1.13-stable-1~deb13u1
Debian:14libeventbefore 2.1.13-stable-12.1.13-stable-1
openSUSE:Tumbleweedlibeventbefore 2.1.13-1.12.1.13-1.1
Red Hat:enterprise_linux:10.2libeventbefore 0:2.1.13-1.el10_20:2.1.13-1.el10_2
Red Hat:enterprise_linux:10.2libevent-debuginfobefore 0:2.1.13-1.el10_20:2.1.13-1.el10_2
Red Hat:enterprise_linux:10.2libevent-debugsourcebefore 0:2.1.13-1.el10_20:2.1.13-1.el10_2
Red Hat:enterprise_linux:10.2libevent-develbefore 0:2.1.13-1.el10_20:2.1.13-1.el10_2
Red Hat:enterprise_linux:10.2libevent-docbefore 0:2.1.13-1.el10_20:2.1.13-1.el10_2
Red Hat:enterprise_linux:8::appstreamlibevent-debuginfobefore 0:2.1.8-11.el8_100:2.1.8-11.el8_10
Red Hat:enterprise_linux:8::appstreamlibevent-debugsourcebefore 0:2.1.8-11.el8_100:2.1.8-11.el8_10
Red Hat:enterprise_linux:8::appstreamlibevent-develbefore 0:2.1.8-11.el8_100:2.1.8-11.el8_10
Red Hat:enterprise_linux:8::baseoslibeventbefore 0:2.1.8-11.el8_100:2.1.8-11.el8_10
Red Hat:enterprise_linux:8::baseoslibevent-docbefore 0:2.1.8-11.el8_100:2.1.8-11.el8_10
Red Hat:enterprise_linux:9::appstreamlibevent-debuginfobefore 0:2.1.13-1.el9_80:2.1.13-1.el9_8

+10

Same product

libevent: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-63382libevent evhttp: Multiple HTTP Parser Bugs Enable Request Smuggling
    37Monitor
  • CVE-2026-63385Libevent: HTTP header handling bugs create risk of access control bypass.
    36Monitor
  • CVE-2026-63384Libevent: `evtag_unmarshal_header()` decodes a wire `uint32` length into a signed `int` return value.
    34Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2026-63380Aug 20, 2026 · Libevent: Null Pointer Dereference in `evws_new_session`
    22Monitor
  • ← EarlierCVE-2026-63381Aug 20, 2026 · Libevent: Dangling Pointer in `evbuffer_add_buffer_reference`
    23Monitor
  • Later →CVE-2026-63387Aug 20, 2026 · Libevent: Off-by-one stack buffer overflow in dnsname_to_labels via crafted DNS server response
    28Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
almalinux:libevent2.1.8-11.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:libevent-devel2.1.8-11.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:libevent-doc2.1.8-11.el8_10 · AlmaLinux:8Package registry (OSV)
debian:libevent2.1.12-stable-8+deb12u1 · Debian:12Package registry (OSV)
opensuse:libevent2.1.13-1.1 · openSUSE:TumbleweedPackage registry (OSV)
red hat:libevent0:2.1.12-19.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:libevent-debuginfo0:2.1.8-11.el8_10 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:libevent-debugsource0:2.1.8-11.el8_10 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:libevent-devel0:2.1.12-19.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:libevent-devel0:2.1.8-11.el8_10 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:libevent-doc0:2.1.12-19.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
rocky linux:libevent0:2.1.8-11.el8_10 · Rocky Linux:8Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Not on record for this CVE: researcher credit · variant or chain candidate · public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
X

Weakness class (CWE)

CWE-125 · Out-of-bounds Read

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

References

Show all references (4 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records