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CVE detail

CVE-2021-23839

OpenSSL 1.0.2 supports SSLv2. If a client attempts to negotiate SSLv2 with a server that is configured to support both SSLv2 and more recent SSL and TLS versions then a check is made for a version rollback attack when unpadding an RSA signature. Clients that support SSL or TLS versions greater than SSLv2 are supposed to use a special form of padding. A server that supports greater than SSLv2 is supposed to reject connection attempts from a client where this special form of padding is present, because this indicates that a version rollback has occurred (i.e. both client and server support greater than SSLv2, and yet this is the version that is being requested). The implementation of this padding check inverted the logic so that the connection attempt is accepted if the padding is present, and rejected if it is absent. This means that such as server will accept a connection if a version rollback attack has occurred. Further the server will erroneously reject a connection if a normal SSLv2 connection attempt is made. Only OpenSSL 1.0.2 servers from version 1.0.2s to 1.0.2x are affected by this issue. In order to be vulnerable a 1.0.2 server must: 1) have configured SSLv2 support at compile time (this is off by default), 2) have configured SSLv2 support at runtime (this is off by default), 3) have configured SSLv2 ciphersuites (these are not in the default ciphersuite list) OpenSSL 1.1.1 does not have SSLv2 support and therefore is not vulnerable to this issue. The underlying error is in the implementation of the RSA_padding_check_SSLv23() function. This also affects the RSA_SSLV23_PADDING padding mode used by various other functions. Although 1.1.1 does not support SSLv2 the RSA_padding_check_SSLv23() function still exists, as does the RSA_SSLV23_PADDING padding mode. Applications that directly call that function or use that padding mode will encounter this issue. However since there is no support for the SSLv2 protocol in 1.1.1 this is considered a bug and not a security issue in that version. 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 1.0.2y (Affected 1.0.2s-1.0.2x).

CVSS 3.7 · LowBuzz score 17.5

Buzz score

Why this CVE is surfacing

Buzz score total 17.5

This all-time snapshot uses the same composite formula as Trending across a 30-year evidence window, rather than a current rolling window.

Buzz score components · mention 11.0 · diversity 6.5 · KEV 0.0 · OTX 0.0 · PoC 0.0
Mention score
11.0
2 evidence mentions in the snapshot
Diversity score
6.5
2 sources across 1 categories
KEV score
0.0
No KEV entry observed
OTX score
0.0
0 OTX pulses
PoC score
0.0
0 repos · best confidence N/A
Best PoC traction
0
Maximum stars on a matched PoC repo

Why it matters now

Mention timeline

Total mentions
0
within the 30d window
Peak daily
0
highest bucket

Evidence

Source links by recency

Newest mentions first
2 source links · newest first
  • The OpenSSL Project addressed three vulnerabilitiesSecurity Affairs

    The OpenSSL Project addressed three vulnerabilities, including two denial-of-service (DoS) issues and a bug in the SSLv2 rollback protection. The OpenSSL Project released security patches to address three vulnerabilities, two denial-of-service (DoS) flaws, and an incorrect SSLv2 rollback protection issue. The fist vulnerability, tracked as CVE-2021-23841, is a NULL pointer dereference issue that can be […]

    newssecurityaffairs.comFeb 18, 2021, 7:07 AM
  • Three New Vulnerabilities Patched in OpenSSLSecurityWeek

    The OpenSSL Project on Tuesday announced the availability of patches for three vulnerabilities, including two that can be exploited for denial-of-service (DoS) attacks and one related to incorrect SSLv2 rollback protection. The most serious of the vulnerabilities , with a severity rating of moderate , is CVE-2021-23841, a NULL pointer dereference issue that can result in a crash and a DoS condition. The security hole is related to a function (X509_issuer_and_serial_hash) that is never called directly by OpenSSL itself, which means it only impacts applications that use the function directly with certificates obtained from untrusted sources. The flaw was reported to OpenSSL developers by Google Project Zero researcher Tavis Ormandy and it has been patched with the release of OpenSSL 1.1.1j. Versions 1.1.1i and earlier are impacted. OpenSSL 1.1.1j also fixes a low-severity integer overflow issue that can also lead to a crash. The bug, tracked as CVE-2021-23840, was identified by Paul Keh…

    newswww.securityweek.comFeb 17, 2021, 9:31 AM

Exploit code

Public exploit repository references

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0 repository references · best confidence N/A · max 0 stars
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