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Fencer Intel
critical 9.1

CVE-2026-4177 json

YAML::Syck versions through 1.36 for Perl has several potential security vulnerabilities including a high-severity heap buffer overflow in the YAML emitter

published 7mo ago modified 3mo ago also EUVD-2026-12523

cvss
9.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 39%
public exploits
0
none known

Summary

YAML::Syck versions through 1.36 for Perl has several potential security vulnerabilities including a high-severity heap buffer overflow in the YAML emitter.

The heap overflow occurs when class names exceed the initial 512-byte allocation.

The base64 decoder could read past the buffer end on trailing newlines.

strtok mutated n->type_id in place, corrupting shared node data.

A memory leak occurred in syck_hdlr_add_anchor when a node already had an anchor. The incoming anchor string 'a' was leaked on early return.

Patch / fix

  • Red Hat Red Hat Enterprise Linux 7 Extended Lifecycle Support 0:1.27-3.el7_9.1
  • Red Hat Red Hat Enterprise Linux 8 0:1.30-6.el8_10
  • libyaml-syck-perl Debian 12 1.34-2+deb12u2
  • libyaml-syck-perl Debian 13 1.34-2+deb13u2
  • libyaml-syck-perl Debian 14 1.36-2

debian advisories DEBIAN-CVE-2026-4177

  • perl-YAML-Syck RHEL 8 1.30-6.el8_10
  • perl-YAML-Syck RHEL 7 ELS 1.27-3.el7_9.1

red hat advisories RHSA-2026:8311RHSA-2026:6470

  • perl-YAML-Syck openSUSE Tumbleweed 1.440.0-1.1

opensuse advisories openSUSE-SU-2026:10551-1

  • perl-YAML-Syck AlmaLinux 8 1.30-6.el8_10

almalinux advisories ALSA-2026:6470

  • perl-YAML-Syck Rocky Linux 8 1.30-6.el8_10

rocky linux advisories RLSA-2026:6470

  • perl-yaml-syck Alpine 3.24 1.45-r0

alpine advisories ALPINE-CVE-2026-4177

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Is CVE-2026-4177 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-4177 updated cvss 7.3

perl-YAML-Syck: YAML::Syck versions through 1.36 for Perl has several potential security vulnerabilities including a high-severity heap buffer overflow in the YAML emitter

  • Red Hat Enterprise Linux 6 perl-YAML-Syck
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux CRB (v. 8) perl-YAML-Syck 1.30-6.el8_10
    fixed: vendor fix RHSA-2026:6470
  • Red Hat Enterprise Linux Server Optional (v. 7 ELS) perl-YAML-Syck 1.27-3.el7_9.1
    fixed: vendor fix RHSA-2026:8311

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
7mo ago

Exploit prediction

0.46% chance of exploitation in the next 30 days, higher than 39% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CISA ADP 3.1 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
CISA ADP 3.1 7.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
CNA 3.1 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
CNA 3.1 7.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

Affected products

  • TODDR YAML::Syck
  • Red Hat Red Hat Enterprise Linux 7 Extended Lifecycle Support
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 6

Classification

Weakness
  • CWE-122 Heap-based Buffer Overflow
  • CWE-120 Buffer Copy without Checking Size of Input

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.