CVE-2021-23840
A public proof of concept exists; no exploitation attested.
- Published2021-02-16
- Fixed in15.10.0 · 12.21.0 · 10.24.0
- WeaknessCWE-190
Am I affected?
Debian, Ubuntu or Red Hat sometimes backport a fix without changing the upstream version number: such a version reads « to verify », never « affected ».With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.
Description
Calls to EVP_CipherUpdate, EVP_EncryptUpdate and EVP_DecryptUpdate may overflow the output length argument in some cases where the input length is close to the maximum permissable length for an integer on the platform. In such cases the return value from the function call will be 1 (indicating success), but the output length value will be negative. This could cause applications to behave incorrectly or crash. OpenSSL versions 1.1.1i and below are affected by this issue. Users of these versions should upgrade to OpenSSL 1.1.1j. OpenSSL versions 1.0.2x and below are affected by this issue. However OpenSSL 1.0.2 is out of support and no longer receiving public updates. Premium support customers of OpenSSL 1.0.2 should upgrade to 1.0.2y. Other users should upgrade to 1.1.1j. Fixed in OpenSSL 1.1.1j (Affected 1.1.1-1.1.1i). Fixed in OpenSSL 1.0.2y (Affected 1.0.2-1.0.2x).
Timeline
dates in UTC- 2021-02-1617:15CVE publishedNVD
- 2026-10-2319:23First public proof of conceptPoC-in-GitHub
- 2026-10-2319:23EPSS crossed 10 %FIRST EPSS
Observed activity
isMalicious corpus · updated 2026-10-23 18:48 UTCBlock these indicators
- Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-23840?format=txt
- CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-23840?format=csv
- TAXII collection of exploited CVEs
- The EDL and CSV take an API key on the Pro plan.
Versions per branch
NVD| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 15.x | ≥ 15.0.0, < 15.10.0 | 15.10.0 | NVD |
| 12.x | ≥ 12.13.0, < 12.21.0 | 12.21.0 | NVD |
| 10.x | ≥ 10.13.0, < 10.24.0 | 10.24.0 | NVD |
| 10.x | ≥ 10.0.0, ≤ 10.12.0 | no fix published | NVD |
| 12.x | ≥ 12.0.0, ≤ 12.12.0 | no fix published | NVD |
| 14.x | ≥ 14.0.0, ≤ 14.14.0 | no fix published | NVD |
| 14.15 | = 14.15.0 | no fix published | NVD |
| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 5.11 | = 5.11.0 | no fix published | NVD |
| 5.11 | = 5.11.1 | no fix published | NVD |
| 5.12 | = 5.12.0 | no fix published | NVD |
| 5.12 | = 5.12.1 | no fix published | NVD |
| 5.13 | = 5.13.0 | no fix published | NVD |
| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 5.5 | = 5.5.0.0.0 | no fix published | NVD |
| 5.9 | = 5.9.0.0.0 | no fix published | NVD |
| 12.2 | = 12.2.1.3.0 | no fix published | NVD |
| 12.2 | = 12.2.1.4.0 | no fix published | NVD |
18 more products in the sources.
as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.
Distribution builds and vendor advisories
Packages from OSV.dev and products from the vendors' CSAF advisories.
version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.
Vendor advisories
Mitsubishi Electric MELSOFT GT OPC UA
GT SoftGOT2000: Versions 1.215Z to 1.270G · MELSOFT GT OPC UA Client: Versions 1.00A to 1.02C
Fix
- Update Node.js to 15.10.0 · 12.21.0 · 10.24.0
- Vendor fix CISA ICSA-22-130-06 · 2 productsUpdate MELSOFT GT OPC UA Client: Update to 1.03D or later
- Mitigation from the vendor CISA ICSA-22-130-06 · 2 productsMitsubishi Electric recommends users update software
- Mitigation from the vendor CISA ICSA-22-130-06 · 2 productsUpdate GT SoftGOT2000: Update to 1.275M or later
- Mitigation from the vendor CISA ICSA-22-130-06 · 2 productsWhen connecting the products to the Internet, use a virtual private network (VPN, etc.) to prevent spoofing and sniffing.
- Mitigation from the vendor CISA ICSA-22-130-06 · 2 productsUse the products within the LAN and block access from untrusted networks and hosts.
- Mitigation from the vendor CISA ICSA-22-130-06 · 2 productsUpdate the OPC UA server to the latest version.
Advisories and patches
- www.openssl.orgVendor Advisory
- www.oracle.comPatch
- www.oracle.comPatch
- www.oracle.comPatch
- www.oracle.comPatch
- www.oracle.comPatch
Detection
read 2026-10-23 19:23 UTC- Nuclei template
- none so far ProjectDiscovery
- Exploit-DB
- no entry Exploit-DB
- Proof-of-concept repositories
- 1 repository, unverifiedTrinadh465/openssl-1.1.1g_CVE-2021-23840 PoC-in-GitHub
Sources
- CISA-ADPSSVC decisionnone2026-04-16
- OpenCVESSVC decisionnone—
- CISA-ADPCVSS 3.17.52026-04-16
- NVDCVSS 3.17.5read 2026-10-23
- NVDCVSS 2.05read 2026-10-23
- CISA-ADPweakness (CWE)CWE-1902026-04-16
- NVDweakness (CWE)CWE-190read 2026-10-23
- FIRST EPSSEPSS score50.7 %read 2026-10-23
- PoC-in-GitHubproof of concept1read 2026-10-23
Technical details
- CVSS v3 Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Published
- 2021-02-16
- Last Modified
- 2026-06-17
- NVD status
- Modified
Frequently asked questions
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