rapidyaml CVE-2026-120455

Exploitation requires the host application to feed an attacker-controlled YAML document into rapidyaml 0.16.0 or earlier, and the document must contain consecutive/excess anchors or tags that exceed the fixed two-element annotation array used by ParseEngine::_add_annotation(). The description specifically scopes the memory corruption to release builds (debug builds likely trip an assertion instead), so the impact manifests in production/release configurations. Exploitation is limited by the local attack vector (AV:L) and required passive user interaction (UI:P) - a victim or application must actually process the malicious document - and by the fact that the attacker needs no authentication but also gains only a crash/memory corruption rather than confidentiality loss.

This is a medium-severity issue (CVSS 4.0 base 6.9) whose signals point to a moderate, non-emergency priority rather than a top-tier threat. The vector (AV:L/AC:L/AT:N/PR:N/UI:P) describes an unauthenticated, low-complexity trigger but requires local delivery and passive user interaction - the host application must process an attacker-supplied YAML document. Impact is dominated by availability (VA:H, a process crash) with only limited integrity impact (VI:L) and no confidentiality impact (VC:N); the evidence confirms stack memory corruption and a crash, not code execution, so the realistic consequence is denial of service. No EPSS score and no CISA KEV listing were provided, so there is no signal of active or widespread exploitation; the vuln.today decision label is 'this_month', consistent with scheduled remediation rather than act_now/emergency. A public PoC reference exists (a hackmd technical write-up plus the VulnCheck advisory and GitHub issue #680), which raises the likelihood of exploitation attempts against exposed parsers, but it is not verified as working weaponized exploit code. Net: a legitimate memory-corruption bug worth patching on a normal cycle, not a high-CVSS-but-illusory issue, though its real-world urgency is bounded by the local vector and the DoS-level impact. Note that an out-of-bounds stack write can in principle enable more than a crash, but the available sources only confirm memory corruption and process termination.

An application that embeds rapidyaml 0.16.0 or earlier parses a YAML document originating from an untrusted source (e.g., an uploaded file or supplied configuration). The attacker crafts a document containing consecutive/excess anchors or tags on a node, overflowing the fixed two-element annotation array in ParseEngine::_add_annotation() and corrupting stack memory, which crashes the process. A public technical write-up describing the flaw exists, though it is not verified as working exploit code.