CVE-2021-40530: The ElGamal implementation in Crypto++ through 8.5 allows plaintext recovery because, during interaction between two cryptographic libraries
Noroxi assessment
Priority: Monitor (action score 23/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 1.1% (FIRST EPSS); higher than 66.9% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
- Fixed version: libcrypto++ (Debian:12) 8.6.0-1; libcryptopp (openSUSE:Tumbleweed) 8.6.0-1.1.
Low priority for now. Upgrade to libcrypto++ (Debian:12) 8.6.0-1; libcryptopp (openSUSE:Tumbleweed) 8.6.0-1.1 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
The ElGamal implementation in Crypto++ through 8.5 allows plaintext recovery because, during interaction between two cryptographic libraries, a certain dangerous combination of the prime defined by the receiver's public key, the generator defined by the receiver's public key, and the sender's ephemeral exponents can lead to a cross-configuration attack against OpenPGP.
- Published
- Sep 6, 2021
- Updated
- Jun 17, 2026
- EPSS
- 1.1% · 66th percentile
- CWE
- CWE-327
Report tools
Action score
23
Monitor
Low priority for now.
- CVSS
- 23 / 40 · 5.9 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 1.1%
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| cryptopp | crypto\+\+ | cpe:2.3:a:cryptopp:crypto\+\+ |
| fedoraproject | fedora | cpe:2.3:o:fedoraproject:fedora |
Check your site's encryption
This vulnerability is about certificate validation or weak cryptography. The free SSL checker tests your certificate, enabled TLS versions and weak ciphers.
Run the SSL checkAffected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- cryptopp crypto++up to 8.5 inclusive
- fedoraproject fedora33
- fedoraproject fedora34
- fedoraproject fedora35
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Debian:12 | libcrypto++ | before 8.6.0-1 | 8.6.0-1 |
| openSUSE:Tumbleweed | libcryptopp | before 8.6.0-1.1 | 8.6.0-1.1 |
Same product
cryptopp: all recordsOther highest-scoring records for the same primary product.
- CVE-2016-3995The timing attack protection in Rijndael::Enc::ProcessAndXorBlock and Rijndael::Dec::ProcessAndXorBlock in Crypto++ (aka cryptopp) before 5.31Monitor
- CVE-2016-9939Crypto++ (aka cryptopp and libcrypto++) 5.6.4 contained a bug in its ASN.1 BER decoding routine.31Monitor
- CVE-2023-50981ModularSquareRoot in Crypto++ (aka cryptopp) through 8.9.0 allows attackers to cause a denial of service (infinite loop) via crafted DER pub30Monitor
Published before and after this one in the same product
- ← EarlierCVE-2017-9434Jun 5, 2017 · Crypto++ (aka cryptopp) through 5.6.5 contains an out-of-bounds read vulnerability in zinflate.cpp in the Inflator filter.22Monitor
- ← EarlierCVE-2019-14318Jul 30, 2019 · Crypto++ 8.3.0 and earlier contains a timing side channel in ECDSA signature generation.24Monitor
- Later →CVE-2021-43398Nov 4, 2021 · Crypto++ (aka Cryptopp) 8.6.0 and earlier contains a timing leakage in MakePublicKey().22Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| debian:libcrypto++ | 8.6.0-1 · Debian:12 | Package registry (OSV) |
| opensuse:libcryptopp | 8.6.0-1.1 · openSUSE:Tumbleweed | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
No history yet (it accumulates with the daily EPSS job).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- high · data can be read
- Integrity
- none
- Availability
- none
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- None
- Availability impact
- None
Weakness class (CWE)
CWE-327 · Use of a Broken or Risky Cryptographic AlgorithmCVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
- Encryption Brute ForcingCAPEC-20likelihood: Low · Low
- Creating a Rogue Certification Authority CertificateCAPEC-459likelihood: Medium · Very High
- Signature SpoofCAPEC-473
- Signature Spoofing by Improper ValidationCAPEC-475likelihood: Low · High
- Cryptanalysis of Cellular EncryptionCAPEC-608High
- Rooting SIM CardsCAPEC-614High
- CryptanalysisCAPEC-97likelihood: Low · Very High
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (4 more)Show less
- ibm.github.io/system-security-research-updates/2021/07/20/insecurity-elgamal-pt1
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/57OJA2K5AHX5HAU2QBDRWLGIIUX7GASC/
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/HGVBZ2TTRKCTYAZTRHTF6OBD4W37F5MT/
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VJYOZGWI7TD27SEXILSM6VUTPPEICDL7/
Vendor advisories and official records. Exploit/PoC links are deliberately left out.