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CVE-2021-33056

24
FAUCET Score

CVE-2021-33056 describes a denial-of-service vulnerability in Belledonne Belle-sip versions prior to 4.5.20, impacting products like Linphone. An attacker can trigger a crash by sending a crafted SIP message containing an invalid From header. This vulnerability carries a high CVSS score of 7.5, indicating a network-based attack with low complexity that can lead to a complete loss of availability. While there is no evidence of active exploitation or public exploit code (Metasploit, Nuclei, ExploitDB), the vulnerability has garnered significant community discussion and media coverage, suggesting awareness within the security community.

Impacted Technologies

VendorProductVersion(s)CPE
< 4.5.20CPE matchmatch criteria
cpe:2.3:a:linphone:belle-sip:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.29%
Probability of exploitation in next 30 days
EPSS Percentile
67.3%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0129 is in the 47th percentile among its peer group of 51,551 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

github_advisorypatch availablevia nvd_reference
View patch

References

github.com / BelledonneCommunications/belle-sip/commit/116e3eb48fe43ea63eb9f3c4b4b30c48d58d6ff0
PatchThird Party Advisory
github.com / BelledonneCommunications/belle-sip/compare/4.5.15...4.5.20
PatchThird Party Advisory