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CVE-2019-11921· NVD / CVE Program· CNA facebook

An out of bounds write is possible via a specially crafted packet in certain configurations of Proxygen due to improper handling of Base64 w

An out of bounds write is possible via a specially crafted packet in certain configurations of Proxygen due to improper handling of Base64 when parsing malformed binary content in Structured HTTP Headers. This issue affects versions of proxygen prior to v2019.07.22.00.

CriticalCVSS 9.8 · v3.0—No exploit No fix recorded
Published
Jul 25, 2019
Updated
Jun 16, 2026
EPSS
2.1% · 81th percentile
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Report tools

JSON

Action score

40

Plan

Add it to your regular patch cycle.

CVSS
39 / 40 · 9.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
1 / 30 · 2.1%

Affected systems

VendorProduct
facebookproxygen

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • facebook proxygenbefore 2019.07.22.00

Versions reported by the vendor

Affected version ranges reported by the assigning authority (facebook). Independent of NVD's CPE analysis and usually ahead of it.

  • Facebook Proxygen

    • v2019.07.22.00affected
    • unspecified and later · before v2019.07.22.00affected

Same product

facebook: all records

Other highest-scoring records for the same primary product.

  • CVE-2020-1897A use-after-free is possible due to an error in lifetime management in the request adaptor when a malicious client invokes request error han
    39Monitor
  • CVE-2019-11940In the course of decompressing HPACK inside the HTTP2 protocol, an unexpected sequence of header table resize operations can place the heade
    39Monitor
  • CVE-2026-44909Proxygen lacked a generalized slow-consumer detection mechanism in its core HTTP session layer.
    30Monitor
  • CVE-2018-6343Proxygen fails to validate that a secondary auth manager is set before dereferencing it.
    30Monitor
  • CVE-2025-55181Sending an HTTP request/response body with greater than 2^31 bytes triggers an infinite loop in proxygen::coro::HTTPQuicCoroSession which bl
    21Monitor
  • CVE-2026-91096In proxygen from v2024.10.28.00 until v2026.09.28.00, WebTransportImpl::terminateSessionStreams (WebTransportImpl::destroy in releases befor
    0Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

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.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, 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.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-787 · Out-of-bounds Write

CVSS vector

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Noroxi analysis

No Noroxi analysis for this record yet

We don't hand-write analysis for all 385,000+ vulnerabilities; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.

We use this product, ask for help

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records