CVE-2025-68113Medium· 6.5▾ SunlitALTCHA is privacy-first software for captcha and bot protection. A cryptographic semantic binding flaw in ALTCHA libraries allows challenge payload splicing, which may enable replay attacks. The HMAC signature does not unambiguously bind…
▾ Sunlit zone — Low / medium · no exploitation signal
impact 35.8 · likelihood 0.1 · exploitation 0
Need a working PoC? Pro members can cast a request and our team develops one — it lands right here.
Exploit-prediction probability, daily snapshots since Aug 1.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
0.3%
0.3% → 0.5%
Last analysed / modified upstream
ALTCHA is privacy-first software for captcha and bot protection. A cryptographic semantic binding flaw in ALTCHA libraries allows challenge payload splicing, which may enable replay attacks. The HMAC signature does not unambiguously bind challenge parameters to the nonce, allowing an attacker to reinterpret a valid proof-of-work submission with a modified expiration value. This may allow previously solved challenges to be reused beyond their intended lifetime, depending on server-side replay handling and deployment assumptions. The vulnerability primarily impacts abuse-prevention mechanisms such as rate limiting and bot mitigation. It does not directly affect data confidentiality or integrity. This issue has been addressed by enforcing explicit semantic separation between challenge parameters and the nonce during HMAC computation. Users are advised to upgrade to patched versions, which include version 1.0.0 of the altcha Golang package, version 1.0.0 of the altcha Rubygem, version 1.0.0 of the altcha pip package, version 1.0.0 of the altcha Erlang package, version 1.4.1 of the altcha-lib npm package, version 1.3.1 of the altcha-org/altcha Composer package, and version 1.3.0 of the org.altcha:altcha Maven package. As a mitigation, implementations may append a delimiter to the end of the salt value prior to HMAC computation (for example, <salt>?expires=<time>&). This prevents ambiguity between parameters and the nonce and is backward-compatible with existing implementations, as the delimiter is treated as a standard URL parameter separator.
Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Affected packages:
altcha-lib < 1.4.1altcha-org/altcha < 1.3.1github.com/altcha-org/altcha-lib-go < 1.0.0org.altcha:altcha < 1.3.0altcha < 1.0.0altcha < 1.0.0altcha < 1.0.0Patched in:
altcha-lib 1.4.1altcha-org/altcha 1.3.1github.com/altcha-org/altcha-lib-go 1.0.0org.altcha:altcha 1.3.0altcha 1.0.0altcha 1.0.0altcha 1.0.0Connected by shared product, vendor, weakness, or advisory.
CVE-2025-55311Medium· 6.5An issue was discovered in Foxit PDF and Editor for Windows and macOS before 13.2 and 2025 before 2025.2
CVE-2025-12295Medium· 6.6A weakness has been identified in D-Link DAP-2695 2.00RC13
CVE-2020-3138Medium· 6.7A vulnerability in the upgrade component of Cisco Enterprise NFV Infrastructure Software (NFVIS) could allow an authenticated, local attacker to install a malicious file when upgrading
CVE-2020-3308Medium· 4.9A vulnerability in the Image Signature Verification feature of Cisco Firepower Threat Defense (FTD) Software could allow an authenticated, remote attacker with administrator-level credentials to install a malicious software patch on an a…
CVE-2024-23680Medium· 5.3AWS Encryption SDK for Java versions 2.0.0 to 2.2.0 and less than 1.9.0 incorrectly validates some invalid ECDSA signatures.
CVE-2026-1529High· 8.1A flaw was found in Keycloak