GoBGP confederation validation panics on empty AS_PATH attribute
cve-program · CVE-2026-49838
PublishedGoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Prior to version 4.7.0, GoBGP accepts a zero-length AS_PATH during UPDATE decoding and later panics while validating that attribute for a confederation eBGP peer. The vulnerable path is in the BGP UPDATE validator: a malformed UPDATE that should be rejected as a malformed AS_PATH instead reaches an unchecked `p.Value[0]` access, allowing a configured confederation eBGP peer to trigger a denial of service. Version 4.7.0 patches the issue.
Read the publisher's advisoryeuvd · EUVD-2026-75807
PublishedGoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Prior to version 4.7.0, GoBGP accepts a zero-length AS_PATH during UPDATE decoding and later panics while validating that attribute for a confederation eBGP peer. The vulnerable path is in the BGP UPDATE validator: a malformed UPDATE that should be rejected as a malformed AS_PATH instead reaches an unchecked `p.Value[0]` access, allowing a configured confederation eBGP peer to trigger a denial of service. Version 4.7.0 patches the issue.
Read the publisher's advisorynvd · CVE-2026-49838
PublishedGoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Prior to version 4.7.0, GoBGP accepts a zero-length AS_PATH during UPDATE decoding and later panics while validating that attribute for a confederation eBGP peer. The vulnerable path is in the BGP UPDATE validator: a malformed UPDATE that should be rejected as a malformed AS_PATH instead reaches an unchecked `p.Value[0]` access, allowing a configured confederation eBGP peer to trigger a denial of service. Version 4.7.0 patches the issue.
Read the publisher's advisoryosv · GHSA-frrj-87jh-2772
PublishedFound through variant analysis based on `CVE-2026-41643` ## Summary GoBGP accepts a zero-length AS_PATH during UPDATE decoding and later panics while validating that attribute for a confederation eBGP peer. The vulnerable path is in the BGP UPDATE validator: a malformed UPDATE that should be rejected as a malformed AS_PATH instead reaches an unchecked `p.Value[0]` access, allowing a configured confederation eBGP peer to trigger a denial of service. ## Affected - Project: gobgp - Repo: https://github.com/osrg/gobgp - Pinned ref: c24629411ba49f160d9dc09126f418218127e016 ## Root cause An established peer's receive path reads BGP bytes from the network connection in `pkg/server/fsm.go:1267`, parses UPDATE bodies through the BGP message decoder, and validates decoded UPDATEs with peer state at `pkg/server/fsm.go:1849`. The UPDATE decoder walks the path-attribute list in `pkg/packet/bgp/bgp.go:15773` and selects the concrete attribute parser from the attacker-controlled attribute type at `pkg/packet/bgp/bgp.go:15855`. For AS_PATH, `PathAttributeAsPath.DecodeFromBytes` returns nil when the decoded attribute length is zero (`pkg/packet/bgp/bgp.go:11533`, `pkg/packet/bgp/bgp.go:11538`), leaving `p.Value` empty rather than reporting a malformed attribute. Validation then dispatches each decoded attribute through `ValidateAttribute` (`pkg/packet/bgp/validate.go:34`); in the confederation eBGP branch, `pkg/packet/bgp/validate.go:162` indexes `p.Value[0]` before checking that any AS_PATH segment was decoded. The eBGP and confederation guards are normal peer-state gates: `pkg/config/oc/util.go:127` defines eBGP as peer AS differing from local AS, `pkg/config/oc/util.go:116` checks confederation membership, and `pkg/server/fsm.go:740` and `pkg/server/fsm.go:741` copy those results into the FSM state used by the validator. ## Reproduction [INT-bgp-gobgp-confed-empty-aspath-panic.zip](https://github.com/user-attachments/files/28203698/INT-bgp-gobgp-confed-empty-aspath-panic.zip) ```bash bash ./poc/run.sh ``` ```text TRIGGERED: confed empty AS_PATH validation panic: runtime error: index out of range ``` The `TRIGGERED` line is the recovered panic fingerprint from the confederation eBGP validation path after a zero-length AS_PATH has decoded successfully. A build failure or any output without that fingerprint would not demonstrate this bug, because the signal is tied to the unchecked AS_PATH segment access. ## Impact A remote unauthenticated peer that is configured as a confederation eBGP neighbor can establish a BGP session and send a single malformed UPDATE containing a syntactically valid AS_PATH attribute header with zero value length. Because the decode path does not turn that empty AS_PATH into a `MessageError`, normal malformed-attribute handling is bypassed and validation panics before GoBGP can return a BGP NOTIFICATION. The demonstrated effect is denial of service for the receive goroutine and peer session, with potential process termination if the panic is not recovered by the runtime path; no memory corruption, data disclosure, authentication bypass, or code execution is claimed. ## Suggested fix ```001-fix.diff diff --git a/pkg/packet/bgp/validate.go b/pkg/packet/bgp/validate.go index 2237afb..f07f4fa 100644 --- a/pkg/packet/bgp/validate.go +++ b/pkg/packet/bgp/validate.go @@ -159,6 +159,9 @@ func ValidateAttribute(a PathAttributeInterface, rfs map[Family]BGPAddPathMode, case *PathAttributeAsPath: if isEBGP { if isConfed { + if len(p.Value) == 0 { + return false, NewMessageError(eCode, eSubCodeMalformedAspath, nil, "empty AS_PATH for confederation eBGP") + } if segType := p.Value[0].GetType(); segType != BGP_ASPATH_ATTR_TYPE_CONFED_SEQ { return false, NewMessageError(eCode, eSubCodeMalformedAspath, nil, fmt.Sprintf("segment type is not confederation seq (%d)", segType)) } ``` ## Resources - https://github.com/osrg/gobgp/blob/c24629411ba49f160d9dc09126f418218127e016/pkg/packet/bgp/bgp.go#L11533-L11540 - https://github.com/osrg/gobgp/blob/c24629411ba49f160d9dc09126f418218127e016/pkg/packet/bgp/validate.go#L159-L164
Read the publisher's advisoryosv · GO-2026-5954
PublishedGoBGP confederation validation panics on empty AS_PATH attribute in github.com/osrg/gobgp
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cve-program · CVE-2026-49838
PublishedGoBGP confederation validation panics on empty AS_PATH attribute
GoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Prior to version 4.7.0, GoBGP accepts a zero-length AS_PATH during UPDATE decoding and later panics while validating that attribute for a confederation eBGP peer. The vulnerable path is in the BGP UPDATE validator: a malformed UPDATE that should be rejected as a malformed AS_PATH instead reaches an unchecked `p.Value[0]` access, allowing a configured confederation eBGP peer to trigger a denial of service. Version 4.7.0 patches the issue.
- Source published
- 10 Sep 2026 21:57:15 UTC
- Source modified
- 11 Sep 2026 20:31:16 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
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CVSS 3.1 · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
euvd · EUVD-2026-75807
PublishedGoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Prior to version 4.7.0, GoBGP accepts a zero-length AS_PATH during UPDATE decoding and later panics while validating that attribute for a c…
GoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Prior to version 4.7.0, GoBGP accepts a zero-length AS_PATH during UPDATE decoding and later panics while validating that attribute for a confederation eBGP peer. The vulnerable path is in the BGP UPDATE validator: a malformed UPDATE that should be rejected as a malformed AS_PATH instead reaches an unchecked `p.Value[0]` access, allowing a configured confederation eBGP peer to trigger a denial of service. Version 4.7.0 patches the issue.
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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.
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datePublished: Sep 10, 2026, 9:57:15 PM
dateUpdated: Sep 11, 2026, 8:31:16 PM
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- Sep 10, 2026, 9:57:15 PM (timezone not stated)
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- Sep 11, 2026, 8:31:16 PM (timezone not stated)
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- 11 Nov 2026 13:05:03 UTC
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- ENISA EUVD · source terms and attribution apply
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EUVD CVSS 3.1 · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
nvd · CVE-2026-49838
PublishedGoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Prior to version 4.7.0, GoBGP accepts a zero-length AS_PATH during UPDATE decoding and later panics while validating that attribute for a c…
GoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Prior to version 4.7.0, GoBGP accepts a zero-length AS_PATH during UPDATE decoding and later panics while validating that attribute for a confederation eBGP peer. The vulnerable path is in the BGP UPDATE validator: a malformed UPDATE that should be rejected as a malformed AS_PATH instead reaches an unchecked `p.Value[0]` access, allowing a configured confederation eBGP peer to trigger a denial of service. Version 4.7.0 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-129
Original publisher date fields
published: 2026-09-10T22:16:57.660
lastModified: 2026-09-16T13:42:46.970
- 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
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- NIST NVD usage terms; underlying source attribution retained
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CVSS 3.1 · [email protected] · Secondary · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
osv · GHSA-frrj-87jh-2772
PublishedGoBGP confederation validation panics on empty AS_PATH attribute
Found through variant analysis based on `CVE-2026-41643` ## Summary GoBGP accepts a zero-length AS_PATH during UPDATE decoding and later panics while validating that attribute for a confederation eBGP peer. The vulnerable path is in the BGP UPDATE validator: a malformed UPDATE that should be rejected as a malformed AS_PATH instead reaches an unchecked `p.Value[0]` access, allowing a configured confederation eBGP peer to trigger a denial of service. ## Affected - Project: gobgp - Repo: https://github.com/osrg/gobgp - Pinned ref: c24629411ba49f160d9dc09126f418218127e016 ## Root cause An established peer's receive path reads BGP bytes from the network connection in `pkg/server/fsm.go:1267`, parses UPDATE bodies through the BGP message decoder, and validates decoded UPDATEs with peer state at `pkg/server/fsm.go:1849`. The UPDATE decoder walks the path-attribute list in `pkg/packet/bgp/bgp.go:15773` and selects the concrete attribute parser from the attacker-controlled attribute type at `pkg/packet/bgp/bgp.go:15855`. For AS_PATH, `PathAttributeAsPath.DecodeFromBytes` returns nil when the decoded attribute length is zero (`pkg/packet/bgp/bgp.go:11533`, `pkg/packet/bgp/bgp.go:11538`), leaving `p.Value` empty rather than reporting a malformed attribute. Validation then dispatches each decoded attribute through `ValidateAttribute` (`pkg/packet/bgp/validate.go:34`); in the confederation eBGP branch, `pkg/packet/bgp/validate.go:162` indexes `p.Value[0]` before checking that any AS_PATH segment was decoded. The eBGP and confederation guards are normal peer-state gates: `pkg/config/oc/util.go:127` defines eBGP as peer AS differing from local AS, `pkg/config/oc/util.go:116` checks confederation membership, and `pkg/server/fsm.go:740` and `pkg/server/fsm.go:741` copy those results into the FSM state used by the validator. ## Reproduction [INT-bgp-gobgp-confed-empty-aspath-panic.zip](https://github.com/user-attachments/files/28203698/INT-bgp-gobgp-confed-empty-aspath-panic.zip) ```bash bash ./poc/run.sh ``` ```text TRIGGERED: confed empty AS_PATH validation panic: runtime error: index out of range ``` The `TRIGGERED` line is the recovered panic fingerprint from the confederation eBGP validation path after a zero-length AS_PATH has decoded successfully. A build failure or any output without that fingerprint would not demonstrate this bug, because the signal is tied to the unchecked AS_PATH segment access. ## Impact A remote unauthenticated peer that is configured as a confederation eBGP neighbor can establish a BGP session and send a single malformed UPDATE containing a syntactically valid AS_PATH attribute header with zero value length. Because the decode path does not turn that empty AS_PATH into a `MessageError`, normal malformed-attribute handling is bypassed and validation panics before GoBGP can return a BGP NOTIFICATION. The demonstrated effect is denial of service for the receive goroutine and peer session, with potential process termination if the panic is not recovered by the runtime path; no memory corruption, data disclosure, authentication bypass, or code execution is claimed. ## Suggested fix ```001-fix.diff diff --git a/pkg/packet/bgp/validate.go b/pkg/packet/bgp/validate.go index 2237afb..f07f4fa 100644 --- a/pkg/packet/bgp/validate.go +++ b/pkg/packet/bgp/validate.go @@ -159,6 +159,9 @@ func ValidateAttribute(a PathAttributeInterface, rfs map[Family]BGPAddPathMode, case *PathAttributeAsPath: if isEBGP { if isConfed { + if len(p.Value) == 0 { + return false, NewMessageError(eCode, eSubCodeMalformedAspath, nil, "empty AS_PATH for confederation eBGP") + } if segType := p.Value[0].GetType(); segType != BGP_ASPATH_ATTR_TYPE_CONFED_SEQ { return false, NewMessageError(eCode, eSubCodeMalformedAspath, nil, fmt.Sprintf("segment type is not confederation seq (%d)", segType)) } ``` ## Resources - https://github.com/osrg/gobgp/blob/c24629411ba49f160d9dc09126f418218127e016/pkg/packet/bgp/bgp.go#L11533-L11540 - https://github.com/osrg/gobgp/blob/c24629411ba49f160d9dc09126f418218127e016/pkg/packet/bgp/validate.go#L159-L164
- Source published
- 9 Jul 2026 23:21:05 UTC
- Source modified
- 10 Sep 2026 03:50:51 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:N/A:H
Publisher rating · MODERATE
osv · GO-2026-5954
PublishedGoBGP confederation validation panics on empty AS_PATH attribute in github.com/osrg/gobgp
GoBGP confederation validation panics on empty AS_PATH attribute in github.com/osrg/gobgp
- Source published
- 24 Jul 2026 18:35:55 UTC
- Source modified
- 24 Jul 2026 19:00:28 UTC
- Saved here
- 24 Oct 2026 13:19:41 UTC
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- 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.