CVE-2025-66038: OpenSC: `sc_compacttlv_find_tag` can return out-of-bounds pointers

Severity: medium (CVSS 6.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-03-30 · updated 2026-06-17
Weakness: CWE-126

Description

OpenSC is an open source smart card tools and middleware. Prior to version 0.27.0, sc_compacttlv_find_tag searches a compact-TLV buffer for a given tag. In compact-TLV, a single byte encodes the tag (high nibble) and value length (low nibble). With a 1-byte buffer {0x0A}, the encoded element claims tag=0 and length=10 but no value bytes follow. Calling sc_compacttlv_find_tag with search tag 0x00 returns a pointer equal to buf+1 and outlen=10 without verifying that the claimed value length fits within the remaining buffer. In cases where the sc_compacttlv_find_tag is provided untrusted data (such as being read from cards/files), attackers may be able to influence it to return out-of-bounds pointers leading to downstream memory corruption when subsequent code tries to dereference the pointer. This issue has been patched in version 0.27.0.

Affected products

OpenSC: before 0.27.0 — fixed in 0.27.0

How to fix

Upgrade to a fixed version: OpenSC 0.27.0. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2025-66038 or the next vulnerability affects your stack