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CVE Record

CVE-2021-43804: Out-of-bounds read when parsing RTCP BYE message in PJSIP

PJSIP is a free and open source multimedia communication library written in C language implementing standard based protocols such as SIP, SDP, RTP, STUN, TURN, and ICE. In affected versions if the incoming RTCP BYE message contains a reason's length, this declared length is not checked against the actual received packet size, potentially resulting in an out-of-bound read access. This issue affects all users that use PJMEDIA and RTCP. A malicious actor can send a RTCP BYE message with an invalid reason length. Users are advised to upgrade as soon as possible. There are no known workarounds.

HighCVSS 7.3Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

PJSIP has a high-severity parsing flaw in its media handling. A malformed RTCP BYE packet can make affected software read past the received packet boundary. For businesses, the concern is exposed voice, video, or SIP media systems using PJMEDIA and RTCP, especially where untrusted peers can send media-control traffic.

Executive priority

Treat as a priority patch for internet-facing or partner-facing communications platforms. The bug is remotely reachable without authentication according to CVSS, and no workaround is named. Urgency is lower for isolated systems where RTCP from untrusted sources cannot reach affected software.

Technical view

CVE-2021-43804 is a CWE-125 out-of-bounds read in pjproject/PJSIP <= 2.11.1. The RTCP BYE reason length is trusted without confirming the packet actually contains that many bytes. The CVSS 3.1 score is 7.3, network exploitable, low complexity, no privileges, and no user interaction.

Likely exposure

Likely exposure is in applications, appliances, or packages embedding pjproject/PJSIP PJMEDIA with RTCP enabled. Distribution advisories in the bundle show downstream security updates for pjproject-linked packages, including Asterisk and Ring. Systems without PJMEDIA/RTCP use are not identified as affected by the supplied sources.

Exploitation context

The supplied CVSS vector supports remote unauthenticated reachability, but the bundle does not state active exploitation. KEV is false. A malicious actor could send a malformed RTCP BYE packet, but the sources do not provide evidence of weaponized exploitation or a public exploit campaign.

Researcher notes

Focus validation on RTCP BYE parsing paths in PJMEDIA and dependency provenance. The key condition is a declared reason length that exceeds the actual received packet size. Avoid assuming exploit impact beyond CVSS low confidentiality, integrity, and availability without environment-specific evidence.

Mitigation direction

  • Upgrade affected pjproject/PJSIP packages from versions <= 2.11.1 using vendor guidance.
  • Apply relevant OS distribution updates for bundled pjproject-dependent packages.
  • Prioritize exposed VoIP, SIP, RTP, and conferencing services using PJMEDIA and RTCP.
  • Where upgrades are unavailable, consult vendor guidance; the source states no known workarounds.
  • Review downstream applications that statically bundle pjproject rather than using system packages.

Validation and detection

  • Inventory pjproject/PJSIP versions and flag versions <= 2.11.1.
  • Confirm whether applications use PJMEDIA and accept RTCP traffic.
  • Check package manager advisories for pjproject, Asterisk, Ring, and related media applications.
  • Verify vendor or distribution security updates are installed in production images.
  • Record compensating network exposure controls separately from vulnerability remediation.
Prepared
Confidence
high
Sources
9

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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cwe · low confidence lookup

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cve · low confidence lookup

CVE-2021-43804 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.3 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
9Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.3CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L3.93.4Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

7.3High
CVSS 3.1 vector shape for CVE-2021-43804Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
pjsippjproject<= 2.11.1Listed
Weakness

CWE details

CWE-125

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.