GoBGP: BGP OPEN capability parser may read capability values outside declared CapLen boundaries
cve-program · CVE-2026-49837
PublishedGoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Versions prior to 4.6.0 contain a BGP OPEN capability parsing issue where several concrete capability decoders may parse data from the full remaining capability buffer instead of the slice bounded by the declared capability length, `CapLen`. A malformed BGP OPEN message can cause bytes from a following capability to be interpreted as part of the current capability. The most security-relevant case is the 4-octet AS capability, where a capability with `CapLen == 0` may cause the parser to read bytes from the following capability as the 4-octet AS value. This parsed value may later affect peer AS validation during BGP session establishment. Version 4.6.0 patches the issue.
Read the publisher's advisoryeuvd · EUVD-2026-75806
PublishedGoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Versions prior to 4.6.0 contain a BGP OPEN capability parsing issue where several concrete capability decoders may parse data from the full remaining capability buffer instead of the slice bounded by the declared capability length, `CapLen`. A malformed BGP OPEN message can cause bytes from a following capability to be interpreted as part of the current capability. The most security-relevant case is the 4-octet AS capability, where a capability with `CapLen == 0` may cause the parser to read bytes from the following capability as the 4-octet AS value. This parsed value may later affect peer AS validation during BGP session establishment. Version 4.6.0 patches the issue.
Read the publisher's advisorynvd · CVE-2026-49837
PublishedGoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Versions prior to 4.6.0 contain a BGP OPEN capability parsing issue where several concrete capability decoders may parse data from the full remaining capability buffer instead of the slice bounded by the declared capability length, `CapLen`. A malformed BGP OPEN message can cause bytes from a following capability to be interpreted as part of the current capability. The most security-relevant case is the 4-octet AS capability, where a capability with `CapLen == 0` may cause the parser to read bytes from the following capability as the 4-octet AS value. This parsed value may later affect peer AS validation during BGP session establishment. Version 4.6.0 patches the issue.
Read the publisher's advisoryosv · GHSA-gjrg-jjr3-56cm
Published### Summary GoBGP contains a BGP OPEN capability parsing issue where several concrete capability decoders may parse data from the full remaining capability buffer instead of the slice bounded by the declared capability length, `CapLen`. A malformed BGP OPEN message can cause bytes from a following capability to be interpreted as part of the current capability. The most security-relevant case is the 4-octet AS capability, where a capability with `CapLen == 0` may cause the parser to read bytes from the following capability as the 4-octet AS value. This parsed value may later affect peer AS validation during BGP session establishment. ### Details The issue is in the BGP OPEN capability parser under: - `pkg/packet/bgp/bgp.go` - `pkg/packet/bgp/validate.go` - The BGP OPEN optional parameter capability format includes a capability code, a capability length field, and a capability value. Each concrete capability decoder should only parse bytes inside the declared capability value boundary. In affected versions, the generic capability parser records the declared `CapLen`, but several concrete capability decoders continue parsing from the full remaining capability buffer after advancing past the two-byte capability header. Conceptually, the vulnerable pattern is: ```go data = data[2:] // decoder reads from data without first limiting it to CapLen ### PoC The following parser-level proof of concept demonstrates the issue without requiring a full BGP session or a running `bgpd` instance. The malformed capability uses: - Capability Code: `65` (`BGP_CAP_FOUR_OCTET_AS_NUMBER`) - Declared `CapLen`: `0` - Four following bytes: `00 00 fd e8` Although the capability declares an empty value, affected versions parse the following four bytes as the 4-octet AS value `65000`. ### Impact A remote peer that can send a malformed BGP OPEN message to a GoBGP instance may cause capability values to be parsed from outside their declared `CapLen` boundaries. In the 4-octet AS capability case, this may affect: - peer AS validation; - capability negotiation; - interpretation of malformed OPEN messages; - acceptance or rejection decisions during BGP session establishment. This issue does not appear to be arbitrary memory corruption, remote code execution, or information disclosure. It is a protocol parser boundary validation issue that can affect BGP OPEN validation semantics.
Read the publisher's advisoryosv · GO-2026-5955
PublishedGoBGP: BGP OPEN capability parser may read capability values outside declared CapLen boundaries in github.com/osrg/gobgp
Read the publisher's advisoryAffected versions, risk and source history
Exploitation and risk
Source statusCISA KEV lists vulnerabilities known to be exploited. FIRST EPSS estimates the likelihood of exploitation in the next 30 days. An unavailable score does not mean zero risk.
Which CVEs have scores here?
This view includes predictions for CVE identifiers explicitly listed in public NuGet advisories. Microsoft release pages have their own prediction coverage. Check source status for the scope and latest checks.
No exploitation or prediction data is available here for these CVEs. This does not mean they are safe or unlikely to be exploited.
cve-program · CVE-2026-49837
PublishedGoBGP: BGP OPEN capability parser may read capability values outside declared CapLen boundaries
GoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Versions prior to 4.6.0 contain a BGP OPEN capability parsing issue where several concrete capability decoders may parse data from the full remaining capability buffer instead of the slice bounded by the declared capability length, `CapLen`. A malformed BGP OPEN message can cause bytes from a following capability to be interpreted as part of the current capability. The most security-relevant case is the 4-octet AS capability, where a capability with `CapLen == 0` may cause the parser to read bytes from the following capability as the 4-octet AS value. This parsed value may later affect peer AS validation during BGP session establishment. Version 4.6.0 patches the issue.
- Source published
- 10 Sep 2026 21:56:13 UTC
- Source modified
- 15 Sep 2026 15:10:15 UTC
- Saved here
- 23 Oct 2026 15:48:27 UTC
- Source terms
- CVE Program Terms of Use
Original source record · Cite this exact observation · Complete original publisher JSON
Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.
CVSS 3.1 · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
euvd · EUVD-2026-75806
PublishedGoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Versions prior to 4.6.0 contain a BGP OPEN capability parsing issue where several concrete capability decoders may parse data from the full…
GoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Versions prior to 4.6.0 contain a BGP OPEN capability parsing issue where several concrete capability decoders may parse data from the full remaining capability buffer instead of the slice bounded by the declared capability length, `CapLen`. A malformed BGP OPEN message can cause bytes from a following capability to be interpreted as part of the current capability. The most security-relevant case is the 4-octet AS capability, where a capability with `CapLen == 0` may cause the parser to read bytes from the following capability as the 4-octet AS value. This parsed value may later affect peer AS validation during BGP session establishment. Version 4.6.0 patches the issue.
Additional publisher context
EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.
Original publisher date fields
datePublished: Sep 10, 2026, 9:56:13 PM
dateUpdated: Sep 15, 2026, 3:10:15 PM
- Source published
- Sep 10, 2026, 9:56:13 PM (timezone not stated)
- Source modified
- Sep 15, 2026, 3:10:15 PM (timezone not stated)
- Saved here
- 11 Nov 2026 13:05:02 UTC
- Source terms
- ENISA EUVD · source terms and attribution apply
Original source record · Cite this exact observation · Complete original publisher JSON
Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.
EUVD CVSS 3.1 · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
nvd · CVE-2026-49837
PublishedGoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Versions prior to 4.6.0 contain a BGP OPEN capability parsing issue where several concrete capability decoders may parse data from the full…
GoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Versions prior to 4.6.0 contain a BGP OPEN capability parsing issue where several concrete capability decoders may parse data from the full remaining capability buffer instead of the slice bounded by the declared capability length, `CapLen`. A malformed BGP OPEN message can cause bytes from a following capability to be interpreted as part of the current capability. The most security-relevant case is the 4-octet AS capability, where a capability with `CapLen == 0` may cause the parser to read bytes from the following capability as the 4-octet AS value. This parsed value may later affect peer AS validation during BGP session establishment. Version 4.6.0 patches the issue.
Additional publisher context
NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.
Source analysis status: Deferred
Weakness classifications: CWE-125
Original publisher date fields
published: 2026-09-10T22:16:57.507
lastModified: 2026-09-16T13:42:46.953
- Source published
- 10 Sep 2026 22:16:57 UTC
- Source modified
- 16 Sep 2026 13:42:46 UTC
- Saved here
- 25 Oct 2026 12:17:38 UTC
- Source terms
- NIST NVD usage terms; underlying source attribution retained
Original source record · Cite this exact observation · Complete original publisher JSON
Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.
CVSS 3.1 · [email protected] · Secondary · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
osv · GHSA-gjrg-jjr3-56cm
PublishedGoBGP: BGP OPEN capability parser may read capability values outside declared CapLen boundaries
### Summary GoBGP contains a BGP OPEN capability parsing issue where several concrete capability decoders may parse data from the full remaining capability buffer instead of the slice bounded by the declared capability length, `CapLen`. A malformed BGP OPEN message can cause bytes from a following capability to be interpreted as part of the current capability. The most security-relevant case is the 4-octet AS capability, where a capability with `CapLen == 0` may cause the parser to read bytes from the following capability as the 4-octet AS value. This parsed value may later affect peer AS validation during BGP session establishment. ### Details The issue is in the BGP OPEN capability parser under: - `pkg/packet/bgp/bgp.go` - `pkg/packet/bgp/validate.go` - The BGP OPEN optional parameter capability format includes a capability code, a capability length field, and a capability value. Each concrete capability decoder should only parse bytes inside the declared capability value boundary. In affected versions, the generic capability parser records the declared `CapLen`, but several concrete capability decoders continue parsing from the full remaining capability buffer after advancing past the two-byte capability header. Conceptually, the vulnerable pattern is: ```go data = data[2:] // decoder reads from data without first limiting it to CapLen ### PoC The following parser-level proof of concept demonstrates the issue without requiring a full BGP session or a running `bgpd` instance. The malformed capability uses: - Capability Code: `65` (`BGP_CAP_FOUR_OCTET_AS_NUMBER`) - Declared `CapLen`: `0` - Four following bytes: `00 00 fd e8` Although the capability declares an empty value, affected versions parse the following four bytes as the 4-octet AS value `65000`. ### Impact A remote peer that can send a malformed BGP OPEN message to a GoBGP instance may cause capability values to be parsed from outside their declared `CapLen` boundaries. In the 4-octet AS capability case, this may affect: - peer AS validation; - capability negotiation; - interpretation of malformed OPEN messages; - acceptance or rejection decisions during BGP session establishment. This issue does not appear to be arbitrary memory corruption, remote code execution, or information disclosure. It is a protocol parser boundary validation issue that can affect BGP OPEN validation semantics.
- Source published
- 9 Jul 2026 23:20:57 UTC
- Source modified
- 24 Jul 2026 19:11:27 UTC
- Saved here
- 24 Oct 2026 13:19:41 UTC
- Source terms
- GitHub Advisory Database · CC-BY-4.0
Original source record · Cite this exact observation · Complete original publisher JSON
Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.
CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Publisher rating · MODERATE
osv · GO-2026-5955
PublishedGoBGP: BGP OPEN capability parser may read capability values outside declared CapLen boundaries in github.com/osrg/gobgp
GoBGP: BGP OPEN capability parser may read capability values outside declared CapLen boundaries in github.com/osrg/gobgp
- Source published
- 24 Jul 2026 18:35:55 UTC
- Source modified
- 24 Jul 2026 19:00:27 UTC
- Saved here
- 24 Oct 2026 13:19:41 UTC
- Source terms
- OSV · upstream source license applies
Original source record · Cite this exact observation · Complete original publisher JSON
Source: osv · OSV · upstream source license applies. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.