CVE-2026-54522: MessagePack::Buffer#clear Use-After-Free that Enables Cross-Buffer Disclosure
Vulnerability summary
CVE-2026-54522 is a medium (CVSS 5.4) Use After Free vulnerability in msgpack messagepack. EPSS estimates a 0.23% chance of exploitation in the next 30 days, higher than 13.4% of scored vulnerabilities. 1 public exploit is recorded.
Not severe (CVSS 2.1, local access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 0 · Related 1Timeline
- 30-07-2026PublishedVulnerability first disclosed.
- 30-07-2026Last modifiedVulnerability information updated.
Description
MessagePack for Ruby is an implementation of the MessagePack binary serialization format. Prior to 1.8.2, MessagePack::Buffer#clear in ext/msgpack/buffer.c leaves rmem_last, rmem_end, and rmem_owner stale after _msgpack_buffer_shift_chunk returns an rmem page to the shared pool, allowing a subsequent Buffer#write and a second MessagePack::Buffer to alias the page and disclose or corrupt cross-buffer data. This issue is fixed in version 1.8.2.
CVSS metrics
9 scores · 7 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated2.1LowCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
- OSV · WolfiEcosystem advisory · calculated2.1LowCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
- OSV · ChainguardEcosystem advisory · calculated2.1LowCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
- OSV · RubygemsEcosystem advisory · calculated2.1LowCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
- NVDNIST2.1LowCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/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
- OSV · UbuntuEcosystem advisory · calculated5.4MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
- OSV · DebianEcosystem advisory · calculated5.4MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
EPSS trend
Probability
0.23%
Chance of exploitation in the next 30 days
Percentile
13%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.23% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
1 foundMsgpack Ruby
Maturity: poc
Weaknesses
CWE · root causeAffected systems
Known conditions: local access, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Chainguard30 products
- commercial-gitlab-rails-ee-19.1All versions (No fix recorded)
- commercial-gitlab-rails-ee-19.2< 19.2.7-r4
- commercial-gitlab-rails-ee-fips-19.1All versions (No fix recorded)
- commercial-gitlab-rails-ee-fips-19.2< 19.2.7-r4
- gitlab-rails-ce-18.1All versions (No fix recorded)
Wolfi3 products
- ruby3.2-fluentd-kubernetes-daemonset-1.19-kinesis< 1.19.2.1.1-r7
- ruby3.2-kube-logging-operator-fluentd-outputs< 6.8.0-r0
- ruby3.4-kube-logging-operator-fluentd-outputs< 6.8.0-r0
Msgpack2 products
- messagepack< 1.8.2
- msgpack-ruby< 1.8.2
Debian1 product
- ruby-msgpackAll versions (No fix recorded) | < 1.8.3-1
RubyGems1 product
- msgpack< 1.8.2
Ubuntu1 product
- ruby-msgpackAll versions (No fix recorded)
6 vendors · 38 products
References
10 links- github.com/msgpack/msgpack-ruby/security/advisories/GHSA-4mrv-5p47-p938X Refsource CONFIRMREPORTAdvisoryWEBExploitVendor Advisory
- github.com/msgpack/msgpack-ruby/commit/5627d71606b565641d2dd501b82aae862f4abe90X Refsource MISCFIXWEBPatch
