CVE-2026-57076: YAML::Syck versions before 1.47 for Perl allow a heap use-after-free via an anchor name reused as an anchors-table key in syck_hdlr_add_anchor

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-16 · updated 2026-10-24
Weakness: CWE-416

Description

YAML::Syck versions before 1.47 for Perl allow a heap use-after-free via an anchor name reused as an anchors-table key in syck_hdlr_add_anchor. In the bundled libsyck an anchor name allocated by syck_strndup is stored both as node->anchor, freed when the node is freed, and as the key in the parser's anchors table. Freeing the node frees the shared key, and a later anchor redefinition makes st_delete compare against the freed key, so st_strcmp reads freed heap memory. Anchors are a standard YAML feature and need no special flags, so this is reached on the default Load path. Any caller that runs Load or LoadFile on an untrusted document that redefines an anchor reaches the read of freed memory.

Affected products

TODDR YAML::Syck: before 1.47 — fixed in 1.47

How to fix

Upgrade to a fixed version: TODDR YAML::Syck 1.47. Check the vendor advisory for mitigations.

References

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